HOW TO PREVENT CANCERS

Soy foods have been studied a great deal for their potential protection against a range of chronic conditions, including breast and prostate cancer, heart disease, osteoporosis, and menopausal symptoms.

It’s not known exactly how a diet rich in soy results in such benefits. It could be due to some of the individual components of soy, such as isoflavones which have some qualities similar to naturally occurring hormones. Or it could be the collective make up of soy, all its components together, which have the beneficial effects.

Because most pre-menopausal symptoms are linked to dropping levels of the hormone estrogen, it’s been considered that soy, and the insoflavones it contains, could help mimic natural estrogen and therefore quell things like hot flashes. Current evidence, though, suggests that soy intake actually has little impact on hormone levels. Still, research also suggest that a diet rich in soy may reduce menopausal symptoms (1).

The potential cardiovascular benefits from higher soy intake may be due to soy’s being a healthier replacement for some higher fat choices. Soy has only about 20 percent of its calories from fat, which is predominantly “healthy” polyunsaturated fat (2), whereas chicken can have nearly half of its calories from fat, and beef can have as much as 80 percent of its calories from fat, much of it in the form of “unhealthy” saturated fat. Studies looking at the relationship between soy intake and heart disease suggest that a diet rich in soy can improve blood pressure, blood cholesterol, and insulin levels (3).

Much of the interest in the links between soy intake and cancer risk is motivated by the historically low breast and prostate cancer risk among Asians, whose diets are traditionally high in soy. Detailed reviews by Wu and colleagues shows that at high intakes typical of Asian diets, soy is significantly related to a reduced risk for breast cancer, and the effect may be strongest for high intake in childhood and adolescence. A meta-analysis found that diets with high amounts of soy (20 mg per day of isoflavone) in Asian women was associated with a decreased risk for breast cancer, compared to Asian women consuming lower amounts (5 mg daily) (4). What this means for most American women is unclear. Studies in the US have typically not found a link between soy intake and breast cancer, but this could largely be due to widely different diets between the two regions. The highest intake in the US is typically 80 percent below the lowest intake in Asia (0.3 mg isoflavones/day in the US versus 25-50 mg isoflavones/day in Asia, which is equivalent to 1 g of soy food versus 80-160 g of soy food). Should diets shift to resemble those of Asia, it’s more than likely that studies would begin to reveal breast cancer benefits with soy as well.

Looking at the data on soy and prostate cancer, a number of studies show benefits from a higher intake of soy and soy-products. Soy milk intake was shown to be inversely related to risk of prostate cancer among US men in the Seventh Day Adventist Cohort study (5). As soy milk consumption went up, the risk of prostate cancer went down. A similar relationship has been seen between total soy intake and the risk of prostate cancer in other cohort and case-control studies (6), even though the amount of the effect on risk varied a bit from study to study. The only potential evidence that soy might increase the risk of prostate cancer comes from research of fermented soy (Miso), which has been positively related to risk in some studies.

Overall, there is currently little evidence that a diet high in soy is bad for health, and a growing body of evidence that it could have substantial health benefits. Realizing such potential benefits though, would likely take intake levels beyond what most people in the US typically eat.


Literature cited:

1. Kurzer, M.S., Soy consumption for reduction of menopausal symptoms. Inflammopharmacology, 2008. 16(5): p. 227-9.
2. van Ee, J.H., Soy constituents: modes of action in low-density lipoprotein management. Nutr Rev, 2009. 67(4): p. 222-34.
3. Carlson, S., et al., Effects of botanical dietary supplements on cardiovascular, cognitive, and metabolic function in males and females. Gend Med, 2008. 5 Suppl A: p. S76-90.
4. Wu, A.H., et al., Epidemiology of soy exposures and breast cancer risk. Br J Cancer, 2008. 98(1): p. 9-14.
5. Jacobsen, B.K., S.F. Knutsen, and G.E. Fraser, Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study (United States). Cancer Causes Control, 1998. 9(6): p. 553-557.
6. Jian, L., Soy, isoflavones, and prostate cancer. Mol Nutr Food Res, 2009. 53(2): p. 217-26.

Numerous recent media reports highlight the historic progress in women's health with development and marketing of oral contraceptives. As Collins reported in the New York Times (column), we celebrate the 50th anniversary of the birth control pill. She notes the need for information on contraception and the challenges women had historically obtaining accurate data. Over the past 50 years much research has focused on contraceptives methods their risks and benefits. As we have noted previously, benefits of oral contraceptives can be substantial. Media attention, however, often focuses on potential adverse effects such as venous thrombosis and pulmonary embolism, the benefits of prevention are not identified at the individual level and hence often ignored.

Contraception avoids not only unintended pregnancies, but also millions of abortions and many pregnancy related deaths. These global benefits are detailed in a report from the Alan Guttmacher Institute in New York. (report). US data indicate that among women 15 to 49 years of age 72.8% are using a method of contraception, 21.2 % repot female sterilization, 9.7% male partner sterilization, and 18% are using contraceptive pills (report).

A rigorous systematic review of contraceptive methods and effectiveness shows that failure varies by approach and by the level of adherence to “perfect use” (review). Combining data from epidemiologic studies show significant reduction in risk of ovarian cancer, endometrial cancer and colon cancer as well as dysfunctional uterine bleeding, and ovarian cysts.

Risk of ovarian cancer is reduced by 20 percent for each 5 years of use. After 15 years of use a woman’s risk is half that of what it would be if she had never user the contraceptive pill. The benefit of reduced ovarian cancer persists after stopping use.

The combined evidence shows without doubt that the pill is safe and has major benefits including a reduction in the level of cancer among users. Like many other prevention benefits, particularly those for cancer, the time course is long and the beneficiaries are largely unknown. This time to benefit clearly contrasts with the immediate benefit related to the indication for using the pill - avoidance of conception – a benefit that is observed each month.  

The New York Times this weekend (story) featured a fascinating article on the role that data and monitoring are increasingly playing in our lives. Among other things, people routinely harness technology to monitor their own physical activity, daily schedules, and diets as well as to identify missed opportunities and potential causes of desirable outcomes. Research has shown that monitoring behaviors can help sustain those behaviors over time, something we discussed in a related post earlier this month (post). The New York Times, though, came at monitoring in a different way, showing how individuals also use monitoring to identify patterns or cause-and-effect relations in their lives - for example, one person used his own productivity data to show that, despite his assumptions, drinking coffee didn’t actually boost his productivity at work.

However people use it, one thing is clear: Data is powerful. This isn’t news. But the ways that data are collected and by whom is important. And although there are myriad minefields to avoid these days as our personal lives play out in an increasingly monitored world, the data that good monitoring provides can also prove invaluable to improving the health and well-being of the nation.

As noted by Dr. Howard Koh, Assistant Secretary of Health and Human Services, in this week’s New England Journal of Medicine, now is a great time to think about data (article). The federal government is about to set forth its own update of health indicators for the nation – something it has done every 10 years since 1979 in the form of the Healthy People initiative – called Healthy People 2020 (official site). Healthy People isn’t just data – it is about setting goals and monitoring our progress toward them using data.