Soy and prostate cancer.
Background: A recent meta-analysis (Yan L 2009) found a significant protective effect of total soy foods (RR/OR = 0.74; 95% CI = 0.63-0.89; P = 0.01), and
nonfermented soy foods (RR/OR = 0.70; 95% CI = 0.56-0.88; P = 0.01) against prostate cancer risk, but no association was found with fermented soy foods
(RR/OR = 1.02; 95% CI = 0.73-1.42; P = 0.92). In addition, a protective effect was found among Asian populations (RR/OR = 0.52; 95% CI = 0.34-0.81; P = 0.01),
but not among Western populations (RR/OR = 0.99; 95% CI = 0.85-1.16; P = 0.91).
This analysis was based on data from 5 cohort studies and 9 case-control studies. Within these populations, a protective effect was found in 1
prospective (Jacobsen BK 1998. Association with soy milk), and 4 case-control studies.
|Reference: Yan L, Spitznagel EL. Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis. Am J Clin Nutr. 2009 Apr;89(4):1155-63. Link.|
Findings: Data about the relation between any soy food and any prostate cancer end point was provided by 9 different cohorts.
In the following tables, data from 2 cohorts (6, 18) is included in which the association with cancer risk was examined, and which were not included in
the meta-analysis (Yan L 2009).
Results: Data is grouped into 3 categories: (total) soy foods, tofu, and miso soup. This leaves data from one cohort examining soy milk (1).
- Total prostate cancer risk: Data about the relation between various soy foods and prostate cancer risk was provided by 7 cohort, including a total of 6,839 cases.
A significant protective effect of soy milk was found in a cohort of small size, including 225 cases (1). No significant association was found in any cohort with (total) soy foods (14, 17-19), tofu (3, 14), or miso soup (3, 6, 14, 19).
In one cohort of very large size, risk was stratified by ethnicity. A significant protective effect of soy products among latinos was found, but not among men from other ethnic groups (17). - Advanced prostate cancer risk: Data about advanced prostate cancer risk was provided by 5 cohorts, including a total of 1,994 cases. A significant protective effect of total soy food against nonlocalized/high grade disease was found in one cohort including 1,278 cases (17), but a significantly increased risk advanced cancer risk of miso soup was found in another cohort including 74 cases (19). No other associations were found with soy milk (1), tofu (3), or soy food (18, 19).
- Prostate cancer mortality: Data about prostate cancer mortality was provided by 2 cohorts, including a total of 345 cases. A significantly increased mortality risk of miso soup was found in one cohort (4). No other associations were found with tofu (20), or miso soup (20).
| Author | Cohort name | Cases | End point | Relative Risk (RR) |
|---|---|---|---|---|
| Iso H (2007) | The JACC Study | 161 | Mortality | HR = 0.95 (0.59-1.51) |
| Kurahashi N (2007) | The JPHC Study | 74 | Advanced prostate cancer | RR = 2.79 (1.19-6.55) |
| Hirayama T (1990) | No cohort name | 183 | Mortality | RR = 1.45 (1.09-1.94) |
| Total number of cases: 418 | Average RR = 1.49 |
Miso soup (fermented soybean paste): The table above shows prospective data about the relation between soybean paste soup and advanced prostate cancer
and/or mortality. 3 cohorts were found which provided data about 418 cases. Significantly increased risks were found in 2 cohorts of moderate-large size and
including 257 cases (including 61% of all cases). No other associations were found.
Conclusion: No evidence was found for an association between either total soy food, tofu, or miso soup and any cancer end point. In addition, no evidence was found
for an association with any cancer end point when total soy, tofu, and miso soup are grouped together. When advanced cancer and mortality are grouped together,
miso soup possibly increases risk (+ 49%). The level of consumption for this effect could not be defined.
Perspective: No evidence was found for an association with total prostate cancer, but RRs for total soy or tofu were all < 1. Findings about advanced stage prostate
cancer and mortality strenghten the evidence of a different effect of non-fermented soy foods vs fermented soy foods.
| More information: back to literature review.|
| Author | Cohort name | Subjects | Years of follow-up | Cases | End point | Consumption of | Relative Risk (RR) | Adjustments | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 19) Kurahashi N (2008) | The Japan Public Health Center-based Prospective Study | 14,203 men aged 40-69 who provided blood samples. (Nested case-control) | 12.8 (1990-93 to 2005) | 201 | Prostate cancer incidence | Soy food (not defined) | No difference in consumptoin was found between cases (61.4) and controls (60.53; P = 0.72). | Age and cohort | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 19) Kurahashi N (2007) | The JPHC Study | 43,509 men aged 45-74. (Japan) | 1995-98 to 2004 | See variables. | Prostate cancer risk | Soy food [Tofu, Yushidofu (pre-drained tofu), Koyadofu (freeze-dried tofu), Aburaage (deep-fried tofu), Natto (fermented soybean), and soymilk] |
Age, area, smoking status, drinking frequency, marital status, BMI, and intake of total fatty acids, dairy, vegetables and fruits. |
18) Kirsh VA. (2007) | The screening arm of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. | 29,361 men aged 55-74. | (USA) mean 4.2 | (1993-2001) 1,338 | of which 520 aggressive (Stage III-IV or gleason score ≥ 7), and ? extraprostatic (Stage III-IV only) prostate cancer risk | Tofu or soybeans | No association either overall or by disease group (aggressive/extraprostetic cancer). | Prostate cancer risk: RR = 0.98 (0.79-1.22; P = 0.63) for the highest vs lowest quartile of consumption. Amount specific data (servings/mo): 0: RR = 1. < 0.5: RR = 1.10 (0.96-1.24). 0.5: RR = 0.86 (0.72-1.03). > 0.5: RR = 0.98 (0.79-1.22). age, total energy, race, study center, family history of prostate cancer, BMI, smoking status, physical activity, supplemental vitamine E intake, total fat intake, red meat intake, diabetes, aspirin use, and previous number of prostate cancer screening examinations during the follow-up period. |
Results were not statistically significantly altered by additional adjustment for total fruit or vegetable intake (as appropriate) and tomato intake or for history of PSA tests before study enrollment. 17) Park SY (2008) | The Multiethnic Cohort Study. | 82,483 men aged 45-75. | 8 | (1993-96 to 2002) Total prostate: 4,404. | Nonlocalized or high-grade: 1,278. Prostate cancer risk (excluding in situ) | Soy products (tofu, miso and vegetarian meat) |
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Time since cohort entry, ethnicity, family history of prostate cancer, education, BMI, smoking status, and energy intake. |
Other potential confounders, such as intake of fruit, vegetables, fat, meat, dairy products, calcium and vitamin D as well as physical activity were not included in the models because these factors were not related to prostate cancer, and did not significantly alter RRs in the current analyses. 14) Allen NE (2004) | The Hiroshima/Nagasaki Life Span Study. | 18,115 men. | (Japan) mean 16.9 | (1963-1996) 193 | Prostate cancer risk | Total soya (the sum of tofu and miso soup intake) |
RR = 0.79 (0.53-1.18; P = 0.23) for the highest vs lowest tertile of consumption. | Amount specific data (times/week): Low: RR = 1. Intermediate: RR = 0.92 (0.64-1.33). High: RR = 0.79 (0.53-1.18). age, calendar period, city of residence, ratiation dose and education level |
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