1. A high ratio of dietary n-6/n-3 polyunsaturated fatty acids is associated
with increased risk of prostate cancer
Christina D. Williamsa,b,c,f,⁎, Brian M. Whitleyc,f
, Cathrine Hoyod
, Delores J. Grante
,
Jared D. Iraggic,f
, Kathryn A. Newmanc,f
, Leah Gerberc,f
, Loretta A. Taylorc,f
,
Madeline G. McKeeverc,f
, Stephen J. Freedlandc,f,g
a
Division of General Internal Medicine, Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA
b
Center for Health Services Research in Primary Care, Durham VA Medical Center, Durham, NC 27705, USA
c
Duke Prostate Center, Division of Urology, Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
d
Department of Community and Family Medicine and the Duke Comprehensive Cancer Center, Durham, NC 27710, USA
e
Cancer Research Program, JLC-Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, NC 27707, USA
f
Department of Surgery, Durham VA Medical Center, Durham, NC 27705, USA
g
Department of Pathology, Duke University School of Medicine, Durham, NC 27710, USA
Received 17 August 2010; revised 28 December 2010; accepted 4 January 2011
Abstract
Experimental studies suggest omega-3 (n-3) polyunsaturated fatty acids (PUFA) suppress and n-6
PUFA promote prostate tumor carcinogenesis. Epidemiologic evidence remains inconclusive. The
objectives of this study were to examine the association between n-3 and n-6 PUFA and prostate
cancer risk and determine if these associations differ by race or disease aggressiveness. We
hypothesize that high intakes of n-3 and n-6 PUFA will be associated with lower and higher prostate
cancer risk, respectively. A case-control study comprising 79 prostate cancer cases and 187 controls
was conducted at the Durham VA Medical Center. Diet was assessed using a food frequency
questionnaire. Logistic regression analyses were used to obtain odds ratios (ORs) and 95%
confidence intervals (95% CI) for the associations between n-3 and n-6 PUFA intakes, the dietary
ratio of n-6/n-3 fatty acids, and prostate cancer risk. Our results showed no significant associations
between specific n-3 or n-6 PUFA intakes and prostate cancer risk. The highest dietary ratio of n-6/
n-3 was significantly associated with elevated risk of high-grade (OR, 3.55; 95% CI, 1.18-10.69;
Ptrend = 0.03), but not low-grade prostate cancer (OR, 0.95; 95% CI, 0.43-2.17). In race-specific
analyses, an increasing dietary ratio of n-6/n-3 fatty acids correlated with higher prostate cancer
risk among white men (Ptrend = 0.05), but not black men. In conclusion, our findings suggest that
a high dietary ratio of n-6/n-3 fatty acids may increase the risk of overall prostate cancer among
white men and possibly increase the risk of high-grade prostate cancer among all men.
© 2011 Elsevier Inc. All rights reserved.
Keywords: Dietary fatty acids; Prostate cancer; Veterans; Race; Case control
Abbreviations: AA, arachidonic acid; ALA, α-linolenic acid; BMI, body mass index; BPH, benign prostate hyperplasia; CI,
confidence interval; EPA, eicosapentaenoic acid; DHA, docosahexanoic acid; FFQ, food frequency questionnaire;
LA, linoleic acid; OR, odds ratio; PSA, prostate-specific antigen; PUFA, polyunsaturated fatty acid.
Available online at www.sciencedirect.com
Nutrition Research 31 (2011) 1–8
www.nrjournal.com
⁎ Corresponding author. Durham VAMC HSR&D, 508 Fulton St (152), Durham, NC 27705, USA. Tel.: +1 919 286 0411x5397; fax: +1 919 416 8025.
E-mail address: christina.williams@duke.edu (C.D. Williams).
0271-5317/$ – see front matter © 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.nutres.2011.01.002

2. 1. Introduction
Prostate cancer is the most commonly diagnosed cancer
among men in the United States [1], and dietary factors are
thought to play a role in prostate cancer development [2].
There is limited evidence that total fat is a risk factor for
prostate cancer [3], and evidence for an association between
specific fatty acids and prostate cancer development or
progression is conflicting [4-10]. The 2 classes of essential
fatty acids are omega-3 (n-3) and omega-6 (n-6) polyunsat-
urated fatty acids (PUFAs). Polyunsaturated fatty acids are
substrates for eicosanoid synthesis, with n-6 fatty acids being
converted into proinflammatory eicosanoids and n-3 PUFA
being converted to anti-inflammatory eicosanoids [4,11].
Animal and in vitro studies suggest that n-3 and n-6 PUFA
have opposite effects on cancer development: n-3 fatty acids,
such as eicosapentaenoic acid (EPA) and docosahexanoic
acid (DHA), suppress tumor carcinogenesis, whereas n-6
PUFA promote development [12]. However, results from
epidemiologic studies, in general, have not confirmed these
findings, with many finding no association between prostate
cancer risk and intake of n-3 or n-6 PUFA [4-8].
One explanation for inconsistent findings among studies is
that the balance of n-3 to n-6 PUFA may be more relevant for
prostate cancer risk than absolute intakes of these fatty acids
[13,14]. The recommended dietary ratio of n-6/n-3 fatty acids
for health benefits is 1:1-2:1 [15], yet the typical Western diet
often contains 10 or more times the amount of n-6 relative to
n-3 PUFA [16]. Alternatively, the relationship between diet
and prostate cancer may differ according to race and
ethnicity. Prostate cancer incidence and mortality rates are
highest among black men [1], yet few studies have focused on
race-specific associations between diet and prostate cancer
risk. Dietary factors may also have stronger associations for
more aggressive prostate cancers [9,17], and this finding
would be missed when all prostate cancers are combined.
The objectives of this study were to examine the
relationship between prostate cancer risk and n-3 and n-6
PUFA intake, and the dietary ratio of n-6/n-3 fatty acids
using a case-control study in veterans and to determine
whether these associations vary by disease aggressiveness
and race. Based on experimental evidence, we hypothesized
that high intake of n-3 PUFA will be associated with lower
risk of prostate cancer, whereas increased intake of n-6
PUFA will correlate with elevated prostate cancer risk.
2. Methods and materials
2.1. Study design and participants
Data collection methods have been described elsewhere
[18]. Briefly, men who had been screened for prostate cancer
in the last 12 months were recruited to participate in an
ongoing case-control study at the Durham Veterans Affairs
Medical Center (DVAMC) in Durham, NC, from January
2007 to November 2009. Cases were men 18 years or older
with no history of prostate cancer who were scheduled for a
prostate needle biopsy at the urology clinic. Of the 485
eligible cases, 450 consented to participate; therefore, the
response rate was 91%. Among those who had the biopsy
done (n = 420), 166 were biopsy positive.
Controls were identified through the urology and internal
medicine clinics at the DVAMC and shared the same
eligibility criteria as cases, with the exception of not being
recommended for a prostate needle biopsy. Of the 421
eligible controls, 307 provided written consent to participate,
yielding a 73% response rate.
Analyses were restricted to participants with complete
questionnaires, and as a result, the analytic sample consisted
of 79 biopsy-positive cases and 187 controls. Cases were
men with biopsy-positive prostate cancer, and healthy
controls were men with no biopsy indication. This study
was approved by the Duke University and DVAMC
Institutional Review Boards.
2.2. Data collection
Anthropometric measurements (weight and height) were
taken by trained personnel. Weight was measured using a
digital scale, and a stadiometer was used to measure height
[19]. These measurements were used to calculate body mass
index (BMI), defined as weight (in kilograms) divided by
the square of height (in meters squared). All questionnaires
were self-administered and typically filled out the day of the
scheduled clinic visit or returned shortly thereafter by mail
prior to the patient knowing the outcome of their biopsy.
Risk factor questionnaires queried information on socio-
demographic characteristics, lifestyle factors such as
smoking and alcohol use, medication use, and family
history of prostate cancer.
Dietary information was obtained using the Harvard food
frequency questionnaire (FFQ), developed and tested for
validity by Willett et al [20] and Holmes et al [21]. This 61-
item food frequency questionnaire assessed the frequency of
consumption as well as the portion size for each food and
beverage item. Subjects reported their intake in the past 12
months, and this time period was selected to account for
seasonal variation in consumption. Daily food, nutrient, and
total energy intakes were determined using the reported
frequency of consumption and portion sizes. The nutrients of
interest for this study were n-3 PUFA (α-linolenic acid
[ALA], EPA, DHA) and n-6 PUFA (arachidonic acid [AA],
linoleic acid [LA]). α-Linolenic acid, the predominant n-3
fatty acid in the Western diet, is found in green leafy
vegetables, nuts, animal meats, and some vegetable oils,
whereas EPA and DHA are abundant in fatty fish and fish
oils [22]. Arachidonic acid is found in animal sources, and
LA is in most vegetable oils and animal meats [22].
2.3. Statistical analyses
Descriptive statistics (means ± SD), medians (interquar-
tile range), and percentages for cases and controls were
2 C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

3. compared using a χ2
test for categorical variables and
Wilcoxon rank sum test for continuous variables. All PUFA
data were represented as the percent of total energy intake.
Correlations between n-3 PUFA and n-6 PUFA were
determined using Pearson correlation coefficients. Each
PUFA was categorized into tertiles, which were based on the
overall distribution of each PUFA among all controls.
Unconditional logistic regression was used to estimate the
odds ratios (ORs) and 95% confidence intervals (95% CIs) of
prostate cancer risk across tertile categories of PUFA intake
relative to the lowest (first) tertile. Odds ratios were adjusted
for factors potentially associated with prostate cancer risk:
age (continuous), BMI (b25, 25-29.9, ≥30 kg/m2
), family
history of prostate cancer (yes/no), smoking status (never,
former, current), total energy (continuous), and, where
appropriate, race (black, white, other). We conducted a
linear trend test by incorporating the median tertile values
among controls into a logistic regression model as a
continuous predictor. To test for interaction, a cross-product
term for race and each PUFA variable was entered into
separate logistic regression models. We then stratified the
models by race to obtain race-specific risk estimates. To
determine the relationship between PUFA intake and disease
aggressiveness, we used multinomial logistic regression to
model the following outcomes: no cancer, low-grade
prostate cancer (Gleason sum b7), and high-grade prostate
cancer (Gleason sum ≥7). Because of our relatively small
sample size, we were unable to perform race-specific
analyses according to disease aggressiveness. All analyses
were done using SAS version 9.2 (SAS Institute, Inc, Cary,
NC), and a P b .05 was considered statistically significant.
3. Results
Compared with controls, prostate cancer cases were more
likely to have a lower BMI (P =.03), and a higher proportion
of cases had a family history of prostate cancer (P =.06;
Table 1). The median prostate-specific antigen (PSA) level
was also higher in cases than controls (P b.0001). There were
no differences in age, education, or smoking status between
cases and controls. There was also no difference between
cases and controls for daily mean intakes of total energy and
PUFA, and the average dietary ratio of n-6/n-3 fatty acids in
cases (9.1) and controls (8.6) was also similar. Table 2 shows
that among n-3 PUFAs, EPA and DHA were nearly perfectly
correlated in cases (r = 0.97) and controls (r = 0.92).
Interestingly, we also observed strong correlations between
n-3 ALA and n-6 LA (r = 0.78 in cases; r = 0.65 in controls).
Overall, we observed no statistically significant associa-
tions between self-reported intakes of total or specific n-3 or
n-6 PUFA and prostate cancer risk among all men combined
(Table 3). Risk estimates for high intakes of the n-3 PUFA
ALA and DHA were similar in combined analyses, yet
neither reached statistical significance. Although n-3 PUFA
EPA and DHA were highly correlated, we did not observe
any statistically significant results when simultaneously
adjusting for EPA and DHA (data not shown). Intake of
total, n-3, and n-6 PUFA remained unrelated to prostate
cancer risk when we examined the associations by race, and
there was no evidence of multiplicative interaction between
race and PUFA intake. The dietary ratio of n-6/n-3 fatty acids
in all men combined was not associated with risk of prostate
cancer. An increasing dietary ratio of n-6/n-3 among white
men appeared to correlate with higher prostate cancer risk
(Ptrend = 0.05), yet no linear trend was observed in black men.
In Table 4, we present risk estimates among all men for
low-grade (Gleason sum b7, n = 43) and high-grade (Gleason
sum ≥7, n = 36) prostate cancer as compared with controls.
We found no evidence of an association or trend between
intake of PUFA and low-grade prostate cancer. There was,
however, a statistically significant elevated risk of high-grade
prostate cancer for men in the highest ratio category of dietary
n-6/n-3 PUFA (OR, 3.55; 95% CI, 1.18-10.69), as well as a
positive linear trend (Ptrend = 0.03).
Table 1
Participant characteristics by case-control status
Cases, n (%) Controls, n (%) P a
n 79 187
Mean (SD) age (y) 63 (6) 62 (7) .34
Race (%) .24
Black 40 (51) 69 (37)
White 38 (48) 112 (60)
Other 1 (1) 4 (2)
Education (%) .34
≤High school 27 (35) 47 (26)
Vocational/technical training 7 (9) 26 (14)
Some College 18 (24) 58 (32)
College graduate/
Advanced degree
24 (32) 52 (28)
BMI (%) .03
b25 kg/m2
14 (18) 22 (12)
25-29.9 kg/m2
34 (44) 56 (31)
≥30 kg/m2
29 (38) 100 (56)
Mean (SD; kg/m2
) 29 (5) 31 (6) .07
Smoking status (%) .17
Current smoker 24 (30) 43 (23)
Former smoker 54 (68) 134 (72)
Never smoker 1 (1) 10 (5)
Family history of
prostate cancer (%)
Yes 19 (24) 27 (14) .06
Median (IQR) PSA (ng/L) 5.8 (4.6-7.5) 0.80 (0.5-1.4) b.0001
Mean (SD) daily intakes
Total energy (kJ)
(% of total energy)
8342 (4930) 7706 (3545) .74
Total n-3 PUFA 0.80 (0.51) 0.76 (0.36) .50
ALA 0.59 (0.28) 0.57 (0.24) .77
EPA 0.09 (0.18) 0.08 (0.12) .89
DHA 0.11 (0.13) 0.10 (0.10) .54
Total n-6 PUFA 6.2 (1.8) 5.9 (1.6) .12
AA 0.09 (0.04) 0.09 (0.04) .19
LA 6.1 (1.9) 5.8 (1.6) .27
n-6/n-3 ratio 9.1 (3.1) 8.6 (2.9) .20
Values are expresses are mean ± SD. IQR indicates interquartile range.
a
Based on Wilcoxon rank sum test for continuous variables and χ2
test
for categorical variables.
3C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

4. Table 2
Pearson correlation coefficients of n-3 and n-6 PUFAs
Cases Controls
ALA EPA DHA AA LA ALA EPA DHA AA LA
n-3 PUFA
ALA 1.00 0.38 ⁎ 0.38 ⁎ -0.04 0.78 ⁎ 1.00 0.22 ⁎ 0.17 -0.01 0.65 ⁎
EPA 1.00 0.97 ⁎ 0.31 ⁎ 0.21 1.00 0.92 ⁎ 0.29 ⁎ 0.04
DHA 1.00 0.40 ⁎ 0.25 ⁎ 1.00 0.52 ⁎ 0.02
n-6 PUFA
AA 1.00 0.05 1.00 0.04
LA 1.00 1.00
⁎ P b.05.
Table 3
ORs and 95% CIs for the association between tertiles of PUFA intake and prostate cancer riska
Combined (n = 266) Black (n = 109) White (n = 150) Pinteraction
Cases OR (95% CI) Cases OR (95% CI) Cases OR (95% CI)
Total PUFA, tertile .34
Tertile 1: b5.7 30 1.00 17 1.00 13 1.00
2: 5.7-7.0 15 0.46 (0.22-0.99) 6 0.25 (0.08-0.82) 9 0.85 (0.29-2.44)
3: 7.1-14.5 34 1.29 (0.67-2.50) 17 1.53 (0.53-4.39) 16 1.34 (0.53-3.42)
Ptrend .38 .39 .52
Total n-3 PUFA .84
1: b0.57 33 1.00 17 1.00 16 1.00
2: 0.57-0.81 21 0.62 (0.31-1.23) 11 0.66 (0.24-1.84) 9 0.53 (0.20-1.47)
3: 0.81-2.6 25 0.83 (0.42-1.63) 12 0.93 (0.32-2.68) 13 0.85 (0.33-2.17)
Ptrend .73 1.00 .87
ALA .01
1: b0.45 30 1.00 16 1.00 14 1.00
2: 0.45-0.58 25 0.75 (0.38-1.48) 15 0.61 (0.22-1.69) 10 0.81 (0.30-2.22)
3: 0.58-1.87 24 0.82 (0.41-1.65) 9 0.46 (0.14-1.49) 14 1.29 (0.50-3.29)
Ptrend .64 .21 .55
EPA .16
1: b0.019 27 1.00 12 1.00 14 1.00
2: 0.019-0.078 25 1.04 (0.53-2.06) 13 1.27 (0.44-3.64) 12 0.98 (0.38-2.53)
3: 0.079-0.83 27 1.13 (0.56-2.24) 15 1.46 (0.51-4.13) 12 0.91 (0.34-2.46)
Ptrend .73 .52 .85
DHA .40
1: b0.054 29 1.00 14 1.00 14 1.00
2: 0.054-0.10 26 0.91 (0.47-1.76) 9 0.55 (0.18-1.68) 17 1.41 (0.59-3.38)
3: 0.10-0.64 24 0.82 (0.40-1.68) 17 0.87 (0.32-2.40) 7 0.58 (0.18-1.91)
Ptrend .60 .99 .43
Total n-6 PUFA .29
1: b5.0 25 1.00 15 1.00 10 1.00
2: 5.0-6.2 18 0.82 (0.39-1.71) 8 0.42 (0.14-1.29) 10 1.72 (0.59-5.03)
3: 6.3-12.5 36 1.62 (0.82-3.17) 17 1.65 (0.58-4.73) 18 1.98 (0.73-5.36)
Ptrend .15 .32 .18
AA .40
1: b0.07 37 1.00 15 1.00 22 1.00
2: 0.07-0.10 23 0.71 (0.37-1.39) 13 0.64 (0.22-1.83) 9 0.57 (0.22-1.50)
3: 0.10-0.26 19 0.52 (0.25-1.08) 12 0.42 (0.14-1.20) 7 0.64 (0.21-1.95)
Ptrend .08 .11 .37
LA .85
1: b4.9 24 1.00 14 1.00 10 1.00
2: 4.9-6.2 20 0.93 (0.45-1.91) 10 0.70 (0.24-2.05) 9 1.22 (0.41-3.59)
3: 6.2-12.5 35 1.60 (0.82-3.15) 16 1.62 (0.56-4.67) 19 2.37 (0.88-6.41)
Ptrend .16 .37 .08
n-6/n-3 ratio .06
1: b7.6 21 1.00 12 1.00 9 1.00
2: 7.6-9.5 23 1.10 (0.53-2.27) 13 0.98 (0.35-2.79) 10 1.17 (0.39-3.50)
3: 9.5-19.0 35 1.57 (0.79-3.11) 15 0.91 (0.32-2.56) 19 2.52 (0.93-6.79)
Ptrend .17 .85 .05
a
Adjusted for age, BMI, family history of prostate cancer, smoking status, total energy, and, in combined analyses, race.
4 C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

5. 4. Discussion
In this case-control study, intakes of total, n-3, and n-6
PUFA were not associated with prostate cancer risk. In
whites, a high dietary ratio of n-6/n-3 fatty acids was
suggestive of higher prostate cancer risk, yet there was a
practically null association between the dietary ratio of n-6/
n-3 fatty acids and prostate cancer risk in blacks. Among all
men, there was evidence of a strong positive association and
significant trend between the dietary ratio of n-6/n-3 fatty
acids and high-grade prostate cancer, whereas this ratio was
unrelated to low-grade prostate cancer. These results do not
confirm the hypothesis that specific dietary n-3 and n-6
PUFA are associated with prostate cancer risk; however,
our findings suggest that the dietary ratio of n-6/n-3 fatty
acids is positively associated with the risk of overall
prostate cancer among white men and high-grade prostate
cancer among all men.
In vitro and animal studies provide evidence that n-3
PUFAs, particularly EPA and DHA, suppress prostate tumor
growth, whereas n-6 PUFA stimulate tumor growth
[13,14,23,24]. The most likely mechanism by which these
fatty acids may affect prostate cancer risk is through the
conversion of n-3 PUFA to anti-inflammatory and n-6 PUFA
to proinflammatory eicosanoids [11]. The n-6 PUFA (AA and
LA) are metabolized into inflammatory eicosanoids, such as
prostaglandin E2, through the cyclooxygenase pathway [25].
The n-3 PUFA EPA and DHA can inhibit this metabolic
pathway and thereby exert their anti-inflammatory properties.
Other possible mechanisms by which n-3 PUFA exhibit
antineoplastic activity include regulating gene expression and
transcription factor activity, altering the production of free
radicals and modulating insulin sensitivity [11].
α-Linolenic acid, the parent fatty acid of all n-3 PUFA,
represents approximately 85% to 94% of total n-3 intake
[26]. Along with n-6 LA, it is 1 of the 2 most frequently
investigated fatty acids potentially associated with prostate
cancer [2]. Our finding regarding the null association
between intake of n-3 ALA and prostate cancer risk is in
agreement with numerous epidemiologic studies showing no
association between ALA and prostate cancer [17,27-30]. A
meta-analysis by Simon et al [7] reported an increased risk of
prostate cancer for high blood and tissue concentrations of
ALA, yet no association between prostate cancer and dietary
ALA was observed. On the contrary, a recent meta-analysis
of 5 prospective studies suggested a small risk reduction for
dietary ALA intakes greater than 1.5 g/d [31].
There is evidence for antiproliferative effects of the n-3
PUFA EPA and DHA [32,33]. In support of these
observations, some epidemiologic studies have observed
inverse associations between EPA and DHA and prostate
cancer risk [9,17,28], whereas others have reported positive
associations [29,34]. The results of our study did not confirm
the hypothesis for a protective effect of these fatty acids.
High intakes of both EPA and DHA were unrelated to
prostate cancer in our study, as was the case in other studies
[10,27,30], one of which was another case-control study in
North Carolina that assessed biomarkers of fatty acid
consumption [10]. Findings for n-6 PUFA have also been
inconsistent, because several studies including ours have
found no evidence for associations between n-6 PUFA and
risk of prostate cancer [8,30,34]. Linoleic acid, the
predominant n-6 fatty acid, has been positively correlated
with elevated prostate cancer risk in some studies [10,35],
although one study reported significant inverse associations
Table 4
ORs and 95% CIs for the association between PUFA intake and low-grade
and high-grade prostate cancer riska
Low-grade prostate
cancer (Gleason sum,
b7; n = 43), OR (95% CI)
High-grade prostate
cancer (Gleason sum,
≥7; n = 36), OR (95% CI)
Total PUFA
Tertile 1 1.00 1.00
2 0.39 (0.15-1.03) 0.54 (0.19-1.54)
3 1.15 (0.52-2.54) 1.43 (0.58-3.57)
Ptrend .65 .40
Total n-3 PUFA
1 1.00 1.00
2 0.69 (0.30-1.59) 0.56 (0.21-1.47)
3 0.93 (0.41-2.10) 0.76 (0.30-1.91)
Ptrend .98 .65
ALA
1 1.00 1.00
2 0.81 (0.36-1.85) 0.74 (0.29-1.90)
3 0.86 (0.37-2.00) 0.87 (0.34-2.24)
Ptrend .77 .82
EPA
1 1.00 1.00
2 1.43 (0.62-3.31) 0.72 (0.28-1.88)
3 1.40 (0.59-3.31) 0.87 (0.34-2.20)
Ptrend .56 .89
DHA
1 1.00 1.00
2 1.01 (0.44-2.32) 0.77 (0.32-1.90)
3 1.15 (0.49-2.70) 0.49 (0.17-1.38)
Ptrend .73 .18
Total n-6 PUFA
1 1.00 1.00
2 0.76 (0.31-1.87) 0.87 (0.30-2.47)
3 1.48 (0.66-3.35) 1.88 (0.74-4.77)
Ptrend .32 .17
AA
1 1.00 1.00
2 0.89 (0.40-1.96) 0.50 (0.20-1.30)
3 0.55 (0.23-1.36) 0.46 (0.17-1.27)
Ptrend .19 .15
LA
1 1.00 1.00
2 1.06 (0.44-2.58) 0.77 (0.28-2.13)
3 1.70 (0.74-3.91) 1.51 (0.61-3.79)
Ptrend .20 .37
n-6/n-3 ratio
1 1.00 1.00
2 0.68 (0.29-1.60) 2.51 (0.78-8.03)
3 0.95 (0.43-2.17) 3.55 (1.18-10.69)
Ptrend .96 .03
a
Adjusted for age, BMI, family history of prostate cancer, smoking
status, total energy, and race.
5C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

6. between LA and the risk of overall, localized, and aggressive
prostate cancer [9].
Omega-3 (n-3) and n-6 PUFA have competing roles in
inflammatory pathways where a high n-3 intake can reduce
the production of proinflammatory eicosanoids derived from
n-6 PUFA, partially because n-3 fatty acids are the
preferential substrates for enzymes involved in eicosanoid
metabolism [11,16]. For this reason, the balance of n-6 and
n-3 PUFA in the diet may have stronger effects on prostate
cancer risk than individual PUFA. Experimental data suggest
that the balance between n-6 and n-3 PUFA can alter the
behavior of prostate tumors [14,23,24,36]. For example,
animal models have shown a growth inhibitory effect on
prostate cancer by lowering the ratio of n-6/n-3 in the diet
[14,36,37]. A recent low-fat dietary intervention trial among
men with prostate cancer reported that lower serum n-6 and/
or higher serum n-3 levels were associated with decreased
proliferation of LNCaP (lymph node cancer of the prostate)
cells when the patient's serum was added to the cancer cells
in vitro [38]. An observational study by Fradet et al [17]
found that a high ratio of long-chain n-3 PUFA (ie, EPA,
DHA, and docosapentaenoic acid) to n-6 PUFA was
associated with a significant lower risk for aggressive
prostate cancer (defined as Gleason sum, ≥7; TNM stage,
NT2; and PSA, ≥10). A high dietary ratio of n-6/n-3 fatty
acids in our study was only suggestive of an elevated risk of
overall prostate cancer; however, there was a significant
positive association with high-grade (ie, aggressive) prostate
cancer. This finding not only supports the idea that the ratio
of n-6 to n-3 fatty acids may be more relevant to prostate
cancer than individual n-6 and n-3 fatty acids but may also
reflect the fact that not all prostate cancers are the same. In
general, studies reporting lower prostate cancer risk with
intakes of n-3 PUFA or fish, the major source of n-3 PUFA,
have observed stronger associations for advanced, aggressive,
or metastatic disease and prostate cancer death [9,39-44].
Furthermore, our findings suggest that the association
between the dietary ratio of these 2 classes of PUFA may
differ between whites and blacks. A positive trend was seen in
white men, whereas no association was observed among black
men. Although we cannot exclude the possibility of a chance
finding, diet-gene interaction is a possible explanation for
this difference. Racial differences in genetic variants of
cyclooxygenase 2, a key enzyme in fatty acid metabolism
may exist and therefore modify the associations between
PUFA and prostate cancer in racial subgroups [45].
Unfortunately, we were unable to assess this interaction in
our study. Other studies have reported different diet and
prostate cancer associations for blacks and whites [43,46].
For example, Hayes et al [43] observed an increased risk of
prostate cancer among whites but not blacks for high intakes
of dairy foods and sweets, whereas high animal fat intake
correlated with increased risk in black s but not whites.
Together, these findings stress the importance of examining
diet and prostate cancer associations separately for different
race/ethnic groups. To our knowledge, our study is the first
to investigate the relationship between PUFA and prostate
cancer risk in a racially diverse sample of US veterans. The
veteran population is ideal for assessing factors that may
contribute to racial disparities due to this system of equal
access to health care.
There are several limitations to our study. Case-control
study designs are often subject to selection bias and recall
bias. Although it is possible that selection bias was
introduced in our results, recall bias is less likely because
cases in our study were interviewed before their biopsy; thus,
they were unaware of their prostate cancer status at the time
of interview which helps to minimize differential recall
between cases and controls. Most findings in this study were
null, and it is not clear whether this stems from a true lack of
association or limited statistical power due to our relatively
small sample size, particularly for stratified analyses.
Measurement error from using a FFQ is possible because
the questionnaire may not have included enough foods to
accurately assess intake of PUFA. In addition, there may
have been insufficient variability in intake in our population
to detect associations with more extreme dietary intakes. For
example, the mean ratio of dietary n-6 to n-3 fatty acids
among controls in our study was 8.6, with a range of 2.7-
19.0. Although this is similar to the average dietary ratio of
n-6/n-3, which is 9.8 in the United States [26], the range in
our study simply represents variations of a Western diet. It
has been suggested that optimal ratios for overall health are
closer to 1:1 or 2:1 [15]; thus, it is possible that not enough
men in the current study had low enough values to show a
substantially lower risk of prostate cancer, though this, of
course, requires further testing. Because our findings were
derived from veterans who had been screened for prostate
cancer, studies in different populations are needed to validate
these findings. This study focused exclusively on prostate
cancer. However, other prostate-related diseases such as
benign prostate hyperplasia (BPH) are also clinically
important as BPH can significantly affect quality of life.
Moreover, BPH has been suggested to be related to diet and
specifically dietary fat intake [47]. We were unable to
address this because our study was developed as a case-
control series of men with prostate cancer, though we hope to
explore this in future studies. Finally, we cannot exclude the
possibility of chance findings due to multiple comparisons
and a lack of strong linear associations with risk.
In summary, we found specific n-3 and n-6 PUFAs intake
to be unrelated to overall prostate cancer risk in this case-
control study among US veterans. There was evidence for an
association between a high dietary ratio of n-6/n-3 PUFA
and increased risk of high-grade prostate cancer, whereas no
specific PUFA or the ratio of PUFA was associated with
low-grade prostate cancer. Our data also suggest that prostate
cancer risk may increase with higher dietary ratios of n-6/n-3
fatty acid intake in white men but not in black men.
Therefore, our findings emphasize the importance of
examining the ratio of n-6 and n-3 PUFA when assessing
the relationship between PUFA intake and prostate cancer
6 C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

7. risk and the need to examine these associations in subgroups
of tumor grade and race/ethnicity.
Acknowledgment
This work was supported by the Agency for Healthcare
Research and Quality (T32 HS00079), National Institutes of
Health NCMHC (P20 MD000175), Department of Defense
(PC060233), Department of Veterans Affairs, and the
American Urological Association Foundation/Astellas Ris-
ing Star in Urology.
References
[1] American Cancer Society. Cancer Facts & Figures 2009. Atlanta (GA):
American Cancer Society; 2009.
[2] Sonn GA, Aronson W, Litwin MS. Impact of diet on prostate cancer: a
review. Prostate Cancer Prostatic Dis 2005;8:304-10.
[3] American Institute for Cancer Research/World Cancer Research Fund.
Food, nutrition, physical activity and the prevention of cancer: a global
perspective. Washington, DC: AICR; 2007.
[4] Terry PD, Rohan TE, Wolk A. Intakes of fish and marine fatty acids
and the risks of cancers of the breast and prostate and of other
hormone-related cancers: a review of the epidemiologic evidence. Am
J Clin Nutr 2003;77:532-43.
[5] Astorg P. Dietary N-6 and N-3 polyunsaturated fatty acids and prostate
cancer risk: a review of epidemiological and experimental evidence.
Cancer Causes Control 2004;15:367-86.
[6] Brouwer IA. Omega-3 PUFA: good or bad for prostate cancer?
Prostaglandins Leukot Essent Fatty Acids 2008;79:97-9.
[7] Simon JA, Chen YH, Bent S. The relation of alpha-linolenic acid to the
risk of prostate cancer: a systematic review and meta-analysis. Am J
Clin Nutr 2009;89:1558S-64S.
[8] Park SY, Wilkens LR, Henning SM, Le Marchand L, Gao K,
Goodman MT, et al. Circulating fatty acids and prostate cancer risk in a
nested case-control study: the Multiethnic Cohort. Cancer Causes
Control 2009;20:211-23.
[9] Chavarro JE, Stampfer MJ, Li H, Campos H, Kurth T, Ma J. A
prospective study of polyunsaturated fatty acid levels in blood and
prostate cancer risk. Cancer Epidemiol Biomarkers Prev 2007;16:
1364-70.
[10] Godley PA, Campbell MK, Gallagher P, Martinson FE, Mohler JL,
Sandler RS. Biomarkers of essential fatty acid consumption and risk of
prostatic carcinoma. Cancer Epidemiol Biomarkers Prev 1996;5:889-95.
[11] Larsson SC, Kumlin M, Ingelman-Sundberg M, Wolk A. Dietary long-
chain n-3 fatty acids for the prevention of cancer: a review of potential
mechanisms. Am J Clin Nutr 2004;79:935-45.
[12] Rose DP. Dietary fatty acids and prevention of hormone-responsive
cancer. Proc Soc Exp Biol Med 1997;216:224-33.
[13] Kelavkar UP, Hutzley J, McHugh K, Allen KG, Parwani A. Prostate
tumor growth can be modulated by dietarily targeting the 15-
lipoxygenase-1 and cyclooxygenase-2 enzymes. Neoplasia 2009;11:
692-9.
[14] Kobayashi N, Barnard RJ, Henning SM, Elashoff D, Reddy ST, Cohen
P, et al. Effect of altering dietary omega-6/omega-3 fatty acid ratios on
prostate cancer membrane composition, cyclooxygenase-2, and
prostaglandin E2. Clin Cancer Res 2006;12:4662-70.
[15] Simopoulos AP. Evolutionary aspects of the dietary omega-6:omega-3
fatty acid ratio: medical implications. World Rev Nutr Diet 2009;100:
1-21.
[16] Daniel CR, McCullough ML, Patel RC, Jacobs EJ, Flanders WD, Thun
MJ, et al. Dietary intake of omega-6 and omega-3 fatty acids and risk
of colorectal cancer in a prospective cohort of U.S. men and women.
Cancer Epidemiol Biomarkers Prev 2009;18:516-25.
[17] Fradet V, Cheng I, Casey G, Witte JS. Dietary omega-3 fatty acids,
cyclooxygenase-2 genetic variation, and aggressive prostate cancer
risk. Clin Cancer Res 2009;15:2559-66.
[18] Antonelli JA, Jones LW, Banez LL, Thomas JA, Anderson K, Taylor
LA, et al. Exercise and prostate cancer risk in a cohort of veterans
undergoing prostate needle biopsy. J Urol 2009;182:2226-31.
[19] Roebuck JA. Anthropometric methods: designing to fit the human
body. Santa Monica (CA): Human Factors and Ergonomics
Society; 1995.
[20] Willett WC, Sampson L, Stampfer MJ, Rosner B, Bain C, Witschi J,
et al. Reproducibility and validity of a semiquantitative food frequency
questionnaire. Am J Epidemiol 1985;122:51-65.
[21] Holmes MD, Powell IJ, Campos H, Stampfer MJ, Giovannucci EL,
Willett WC. Validation of a food frequency questionnaire measure-
ment of selected nutrients using biological markers in African-
American men. Eur J Clin Nutr 2007;61:1328-36.
[22] Meyer BJ, Mann NJ, Lewis JL, Milligan GC, Sinclair AJ, Howe PR.
Dietary intakes and food sources of omega-6 and omega-3 polyunsat-
urated fatty acids. Lipids 2003;38:391-8.
[23] Rose DP, Connolly JM. Effects of fatty acids and eicosanoid synthesis
inhibitors on the growth of two human prostate cancer cell lines.
Prostate 1991;18:243-54.
[24] Pandalai PK, Pilat MJ, Yamazaki K, Naik H, Pienta KJ. The effects of
omega-3 and omega-6 fatty acids on in vitro prostate cancer growth.
Anticancer Res 1996;16:815-20.
[25] Reese AC, Fradet V, Witte JS. Omega-3 fatty acids, genetic variants in
COX-2 and prostate cancer. J Nutrigenet Nutrigenomics 2009;2:
149-58.
[26] Kris-Etherton PM, Taylor DS, Yu-Poth S, Huth P, Moriarty K, Fishell
V, et al. Polyunsaturated fatty acids in the food chain in the United
States. Am J Clin Nutr 2000;71:179S-88S.
[27] Park SY, Murphy SP, Wilkens LR, Henderson BE, Kolonel LN. Fat
and meat intake and prostate cancer risk: the multiethnic cohort study.
Int J Cancer 2007;121:1339-45.
[28] Koralek DO, Peters U, Andriole G, Reding D, Kirsh V, Subar A, et al. A
prospective study of dietary alpha-linolenic acid and the risk of prostate
cancer (United States). Cancer Causes Control 2006;17:783-91.
[29] Wallstrom P, Bjartell A, Gullberg B, Olsson H, Wirfalt EA.
Prospective study on dietary fat and incidence of prostate cancer
(Malmo, Sweden). Cancer Causes Control 2007;18:1107-21.
[30] Hodge AM, English DR, McCredie MR, Severi G, Boyle P, Hopper
JL, et al. Foods, nutrients and prostate cancer. Cancer Causes Control
2004;15:11-20.
[31] Carayol M, Grosclaude P, Delpierre C. Prospective studies of dietary
alpha-linolenic acid intake and prostate cancer risk: a meta-analysis.
Cancer Causes Control 2010;21:347-55.
[32] Rose DP. Effects of dietary fatty acids on breast and prostate cancers:
evidence from in vitro experiments and animal studies. Am J Clin Nutr
1997;66:1513S-22S.
[33] Connolly JM, Coleman M, Rose DP. Effects of dietary fatty acids on
DU145 human prostate cancer cell growth in athymic nude mice. Nutr
Cancer 1997;29:114-9.
[34] Crowe FL, Allen NE, Appleby PN, Overvad K, Aardestrup IV,
Johnsen NF, et al. Fatty acid composition of plasma phospholipids and
risk of prostate cancer in a case-control analysis nested within the
European Prospective Investigation into Cancer and Nutrition. Am J
Clin Nutr 2008;88:1353-63.
[35] Hedelin M, Chang ET, Wiklund F, Bellocco R, Klint A, Adolfsson J,
et al. Association of frequent consumption of fatty fish with prostate
cancer risk is modified by COX-2 polymorphism. Int J Cancer 2007;
120:398-405.
[36] Kelavkar UP, Hutzley J, Dhir R, Kim P, Allen KG, McHugh K.
Prostate tumor growth and recurrence can be modulated by the omega-
6:omega-3 ratio in diet: athymic mouse xenograft model simulating
radical prostatectomy. Neoplasia 2006;8:112-24.
[37] Lloyd JC, Masko EM, Antonelli JA, Phillips TE, Thomas JA, Poulton
SH, Aronson WJ, Freedland SJ, editors. Does type of dietary fat
7C.D. Williams et al. / Nutrition Research 31 (2011) 1–8

8. matter? Prostate cancer xenograft progression in a SCID mouse model
with varying dietary fat sources. [Abstract] In: AUA Annual Meeting
Program Abstracts. J Urol 2010;183(suppl 1):e40.
[38] Aronson WJ, Barnard RJ, Freedland SJ, Henning S, Elashoff D,
Jardack PM, et al. Growth inhibitory effect of low fat diet on
prostate cancer cells: results of a prospective, randomized dietary
intervention trial in men with prostate cancer. J Urol 2010;183:
345-50.
[39] Chavarro JE, Stampfer MJ, Hall MN, Sesso HD, Ma J. A 22-y
prospective study of fish intake in relation to prostate cancer incidence
and mortality. Am J Clin Nutr 2008;88:1297-303.
[40] Leitzmann MF, Stampfer MJ, Michaud DS, Augustsson K, Colditz
GC, Willett WC, et al. Dietary intake of n-3 and n-6 fatty acids and the
risk of prostate cancer. Am J Clin Nutr 2004;80:204-16.
[41] Freeman VL, Meydani M, Hur K, Flanigan RC. Inverse association
between prostatic polyunsaturated fatty acid and risk of locally
advanced prostate carcinoma. Cancer 2004;101:2744-54.
[42] Augustsson K, Michaud DS, Rimm EB, Leitzmann MF, Stampfer
MJ, Willett WC, et al. A prospective study of intake of fish and
marine fatty acids and prostate cancer. Cancer Epidemiol Biomarkers
Prev 2003;12:64-7.
[43] Hayes RB, Ziegler RG, Gridley G, Swanson C, Greenberg RS,
Swanson GM, et al. Dietary factors and risks for prostate cancer among
blacks and whites in the United States. Cancer Epidemiol Biomarkers
Prev 1999;8:25-34.
[44] Terry P, Lichtenstein P, Feychting M, Ahlbom A, Wolk A. Fatty fish
consumption and risk of prostate cancer. Lancet 2001;357:1764-6.
[45] Simopoulos AP. Genetic variants in the metabolism of omega-6 and
omega-3 fatty acids: their role in the determination of nutritional
requirements and chronic disease risk. Exp Biol Med (Maywood)
2010;235:785-95.
[46] Rodriguez C, McCullough ML, Mondul AM, Jacobs EJ, Chao A, Patel
AV, et al. Meat consumption among black and white men and risk of
prostate cancer in the Cancer Prevention Study II Nutrition Cohort.
Cancer Epidemiol Biomarkers Prev 2006;15:211-6.
[47] Barnard RJ, Kobayashi N, Aronson WJ. Effect of diet and exercise
intervention on the growth of prostate epithelial cells. Prostate Cancer
Prostatic Dis 2008;11:362-6.
8 C.D. Williams et al. / Nutrition Research 31 (2011) 1–8