Welcome to Weekly Health Update

“A critical weekly review of important new research findings for health-conscious readers”

SOY ISOFLAVONES REDUCE BREAST CANCER

RECURRENCE RISK

Regular readers of this column are already aware of the controversy surrounding soy isoflavone intake and breast cancer risk.  As happens frequently in clinical research (unfortunately), contradictory research findings have made it difficult to understand the true relationship between dietary soy intake and breast cancer risk (if one exists).  There is, for example, both laboratory and clinical data suggesting that a diet rich in soybean-derived products may be associated with a lower risk of developing breast cancer.  At the same time, because genistein and other dietary isoflavones are known to weakly mimic the effects of estrogen, there has been some concern that a diet rich in isoflavone “phytoestrogens” may increase both the risk of developing a new breast cancer and the risk of developing a recurrence of a previous breast cancer.  (In fact, there is data from laboratory research studies showing that genistein can indeed fuel the growth of human breast cancer cells growing in culture dishes, when exposed to high concentrations of this soy-derived isoflavone.)

A growing body of public health research, primarily from Asian countries where tofu and other soy-based foods are frequently consumed, appears to link increased soy consumption with a decreased lifetime breast cancer risk, particularly when soy-based foods are consumed during adolescence, during the time when development of the female breast is most active (Soy & Breast Cancer Risk).  (Interestingly, there is also recent research suggesting that soy products might also reduce the risk of prostate cancer, which is another hormonally driven cancer:   Genistein & Prostate Cancer Cells, Dietary Soy & Prostate Cancer Risk.)

Although epidemiological research is, increasingly, suggesting that a diet rich in soybean-derived foods might lower a woman’s lifetime risk of developing breast cancer, many breast cancer experts have remained apprehensive regarding dietary isoflavone intake in women with a prior history of breast cancer, in view of the estrogen-like effects of these “phytoestrogens.”  As I have already noted, there is considerable research data available to suggest that soy-derived isoflavones can, at least under certain laboratory conditions, stimulate estrogen-sensitive breast cancer cells to grow and divide.  These research findings have left many oncologists feeling uncomfortable in recommending soy-based foods to their breast cancer patients.  Now, a newly publish public health study in the Journal of the American Medical Association suggests that soy-based foods may actually reduce the risk of breast cancer recurrence, and death due to any cause, in women who have previously been diagnosed with this very common form of cancer.

In this study, which was performed in Shanghai, China, 5,042 female breast cancer survivors (ages 20 to 75 years) were followed for an average of almost 4 years.  All of these patient volunteers underwent detailed surveys regarding their lifestyle habits, including their diets.  These patients, who were originally diagnosed with breast cancer between 2002 and 2006, were surveyed at 6, 18, 36 and 60 months following their original diagnosis with breast cancer.  

The results of this study indicate that the breast cancer survivors who consumed the greatest amount of soy-based foods in their daily diets were 32 percent less likely to experience a recurrence of their breast cancer when compared to the women who consumed the least amount of soy-based isoflavones.  Moreover, the women who consumed the greatest amount of soy were also 29 percent less likely to die, from any cause, when compared to the women who consumed the least amount of soy-derived foods.

A particularly interesting and unexpected finding of this study was that both women with estrogen sensitive breast cancers and women with tumors that were not sensitive to estrogen appeared to experience a significantly decreased risk of breast cancer recurrence if they frequently consumed soy products.  Another important finding of this study was that women who were taking the estrogen-blocking cancer treatment drug tamoxifen also appeared to enjoy a reduced risk of breast cancer recurrence with higher levels of dietary soy intake.  Additionally, the researchers noted that high levels of soy intake appeared to be about as effective in reducing the risk of breast cancer recurrence as the breast cancer prevention drug tamoxifen, alone.

The results of this very important study mirror the findings of the only other prospective clinical study that has looked at the impact of soy-based foods on breast cancer recurrence (the “Life After Cancer Epidemiology,” or “LACE,” study).  The LACE study, which was performed in the United States, followed nearly 2,000 breast cancer survivors for, on average, more than 6 years.  In the LACE study, women who were taking tamoxifen, and who also consumed the highest amount of soy-based dietary isoflavones, were 50 percent less likely to develop a recurrence of their breast cancer when compared to women who reported the lowest consumption of soy-derived foods.

As I have pointed out previously, epidemiological research studies based upon dietary surveys are susceptible to several types of bias which, in turn, can cause researchers to draw the wrong conclusions.  In this case, however, there are now two large prospective cohort studies that have reached essentially the same conclusions (albeit with a rather limited duration of patient follow-up).  Both studies strongly suggest that high levels of soy-based isoflavones in the diet may be able to significantly reduce the risk of breast cancer recurrence.  Based upon the findings of this large Chinese study, the apparent cancer risk reduction effect associated with high levels of soy intake also appears to benefit premenopausal and postmenopausal women, as well as women who are taking the estrogen-blocking drug tamoxifen, women with estrogen-sensitive tumors, and women with (counter-intuitively) estrogen-resistant tumors.

In view of the limited duration of patient follow-up in both of these clinical breast cancer studies, as well as the limitations of survey-based epidemiological research in general, I would like to see updated data from both of these studies after at least 10 years of patient observation before I would be willing to tell my breast cancer patients that they should significantly increase their dietary soy intake.  On the other hand, the rather compelling data presented by both of these clinical research studies will also make me less anxious when any of my breast cancer patients decide, of their own accord, to increase their intake of soy-derived isoflavones.

Note:  Weekly Health Update is currently undergoing an extensive upgrade to better serve its tens of thousands of health-conscious readers around the world.  Beginning in January 2010, newly archived columns will be available by selecting the “Archives” tab on the right side of your screen (all archived columns prior to January 2010 will continue to be available by selecting the “Archives 2007-2009” tab at the top of the screen.)

Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity

Welcome to Weekly Health Update

“A critical weekly review of important new research findings for health-conscious readers”

Salt (Sodium) Intake, Stroke & Cardiovascular Disease

Table salt consists of the elements sodium and chloride, both of which are essential for life.  There is a great deal of clinical research suggesting that more than 5 to 6 grams of salt intake per day (which is equal to 2 to 2.4 grams of sodium)  is associated with a significant increase in the risk of developing high blood pressure which, in turn, is associated with a significantly increased risk of stroke and cardiovascular disease.  Unfortunately, in most countries, the average daily salt intake for adults is considerably greater than 6 grams per day.  Moreover, in many countries of the world, the average daily adult intake of salt is a whopping 12 grams per day, or almost 5 grams of sodium per day. 

In the United States, the American Heart Association (AHA) currently recommends no more than 2.3 grams of sodium intake per day (equivalent to 5 grams, or about one teaspoon, of salt per day).  At the same time, the AHA also states that the ideal daily intake of sodium should actually be about 1.5 grams per day but, in an acknowledgment regarding the high intake of salt-rich processed foods in the United States, the AHA considers the 2.3 gram per day dietary sodium target to be more “realistic” for Americans.

There is considerable public health research data suggesting that the reduction of average daily adult salt intake, to 6 grams per day, or less, would result in a significant lowering of blood pressure in both people with and without high blood pressure.  Based upon these research findings, some public health experts have predicted that lowering the average daily salt intake below 6 grams per day could reduce the incidence of stroke by almost 25 percent, and the incidence of cardiovascular disease by almost 20 percent.  Unfortunately, there have not been any large-scale prospective, randomized, placebo-controlled clinical research trials performed to validate these estimates.  On the other hand, there have been multiple short-term prospective public health trials that have followed groups (cohorts) of patients in terms of their dietary intake of salt and the incidence of stroke and cardiovascular disease events.  Now, a newly published research study, in the British Medical Journal, has performed a meta-analysis of 13 of these “prospective cohort” studies, encompassing a total of 177,025 patient volunteers, with average durations of patient follow-up ranging from 4 to 19 years.  (Meta-analysis is a method of combining the data from multiple different clinical studies into a single “super-study,” in an effort to improve the validity of the resulting data, as well as the conclusions that are reached from such data.)

Among these more than 177,000 patient volunteers, there were 11,000 “vascular events” observed, including stroke and heart attacks (myocardial infarctions).  When the incidence of these vascular events was analyzed, along with dietary salt intake, the patients with the highest daily salt intake were observed to experience a 23 percent greater risk of stroke, and a 17 percent greater risk of cardiovascular disease, when compared to the adults who consumed less salt on a daily basis.

The increasing consumption of salt-rich processed foods throughout both the developed and underdeveloped countries of the world has been pushing daily salt intake to ever higher levels, with many Western countries reporting average daily adult salt intake of nearly 10 grams per day.  In other countries, and most notably in Asia and Eastern Europe, dietary practices that include a high concentration of heavily salted foods have pushed daily salt intake into the 10 to 12 gram per day range for the average adult.

The World Heart Federation estimates that there are 5.5 million annual deaths from stroke across the globe, and an additional 17.5 million annual deaths from cardiovascular disease.  Based upon the increased incidence of stroke and cardiovascular disease predicted by this meta-analysis study, even a rather modest decrease in the average adult daily salt intake, to the World Health Organization’s target of 5 grams per day, should result in 1.25 million fewer deaths per year from stroke and nearly 3 million fewer annual deaths from cardiovascular disease around the world.  Needless to say, this is a tremendous potential public health dividend from a rather simple alteration in our dietary habits.  (On the surface, reducing our daily salt intake would appear to be a rather simple goal.  However, the more complicated reality is that to achieve even the World Health Organization’s rather liberal target of 5 grams of salt per day, our entire food chain would have to be comprehensively reexamined and overhauled.) 

The world’s increasing consumption of highly-processed foods, which often contain high levels of salt as a preservative, are largely responsible for the high levels of salt intake in the developed world (in addition to a preference for salt-cured foods in much of Asia and Eastern Europe).  In the United States, the sodium content of most processed foods is readily available on food packages.  Unfortunately, most restaurants in the United States have not been as forthcoming about the sodium content of the food on their menus (as well as other important nutritional information), and so it continues to be very difficult to determine the actual salt content of much of what we eat here in the United States and, indeed, throughout much of the world.

Note:  Weekly Health Update is currently undergoing an extensive upgrade to better serve its tens of thousands of health-conscious readers around the world.  Beginning in January 2010, newly archived columns will be available by selecting the “Archives” tab on the right side of your screen (all archived columns prior to January 2010 will continue to be available by selecting the “Archives 2007-2009” tab at the top of the screen.)

Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity

Welcome to Weekly Health Update

“A critical weekly review of important new research findings for health-conscious readers”

EXERCISE & PROSTATE CANCER RISK

There is an increasing body of research evidence to suggest that many cases of cancer can be prevented through lifestyle and diet modifications.  Indeed, even conservative estimates suggest that more than 60 percent of new cancer cases could be prevented simply by abstaining from unhealthy lifestyle and dietary habits.  (More enthusiastic cancer prevention experts have suggested that 80 percent of cancer cases, or more, might be preventable with rigorous lifestyle and diet changes.)   Given that, in the best case, modern cancer treatment results in the long-term survival of only about 60 percent of all cancer patients, and that the survival rate for many of the most lethal cancers still remains far more dismal, an ounce of cancer prevention is certainly worth much more than a pound of cancer cure.  (This simple yet profound realization is the central theme of my new book, “A Cancer Prevention Guide for the Human Race,” which will be published in the spring of 2010.) 
 
As a practicing comprehensive Surgical Oncologist, I routinely treat patients with highly lethal cancers, many of which are, sadly, incurable by the time they are diagnosed.  While not every case of cancer can be prevented through lifestyle and diet modification, many of the terrible, and ultimately fatal, cancer cases that I routinely see might have been prevented with reasonably moderate alterations in the way that people choose to live their daily lives.
 
Prostate cancer is the most common non-skin cancer that occurs in men, and the second most common cause of cancer death in men.  In 2009, an estimated 192,000 new cases of prostate cancer will be diagnosed, and approximately 27,000 men will die of this disease.  Prostate cancer currently afflicts 1 out of every 6 American men during their lifetimes, and accounts for 25 percent of all cancer diagnoses in men (similar, I might add, to the percentage of breast cancer cases among all cancer cases diagnosed in women).  Most prostate cancers are stimulated to grow and spread by testosterone and other androgens produced by the testes, and by other tissues in the body. 
 
The relationship between prostate cancer risk and exercise has not been entirely clear, thus far, as various clinical studies have produced contradictory findings.  Some of these studies have suggested that high levels of daily physical activity may reduce the risk of prostate cancer, while other studies have not confirmed a link between prostate cancer risk and physical activity levels.
 
A new prospective public health study, just published in the British Journal of Cancer, adds further important evidence that increased levels of physical activity may indeed reduce the risk of developing prostate cancer.  In this newly published study, nearly 46,000 men between the ages of 45 and 70 years were prospectively followed between 1998 and 2007.  All of these male volunteers completed extensive questionnaires regarding their daily levels of physical activities at 30 years of age and at 50 years of age, as well as at the time or their entry into this clinical study.  These questionnaires specifically included questions regarding walking or bicycling; current waist, hip and height measurements; education level; cigarette smoking; alcohol consumption; diabetes; family history of prostate cancer; and other lifestyle factors.  Six predefined activity levels for occupational activity (from “mostly sitting down” to “heavy manual labor”), and additional predefined categories for time spent on different activities, were specifically included in the questionnaire, such as walking or bicycling (“hardly ever” to “more than 90 min per day”), home or household work (“less than 1 hour per day” to “more than 8 hours per day”), inactive leisure time (“from 2 hours per day or less” to “5 hours per day or more”), and active leisure-time exercising (“from less than 1 hour per week” to “more than 5 hours per week”).  The patient volunteers were also queried regarding the average number of hours per day they spent sleeping. 
 
Importantly, the researchers conducting this study took the extra step of conducting 7-day physical activity evaluations to verify that the study’s participants actually engaged in the levels of physically activity that they claimed on the questionnaires.  (This additional validation step confirmed the accuracy of the questionnaire information supplied by the study’s volunteers.)  The incidence of prostate cancer, and the death rate associated with prostate cancer, among these 45,887 middle-aged and elderly men were then analyzed at the conclusion of this very large prospective epidemiological study. 
 
When the men who engaged in physical activity at the highest levels were compared with those at the lowest levels, some very important differences in prostate cancer risk emerged.  Overall, very high levels of physical activity were associated with a 16 percent reduction in the risk of developing prostate cancer.  Additionally, among the men who spent at least half of their work days being physically active, the risk of prostate cancer was 20 percent lower when compared to men who spent most of their work day sitting down.  Specifically, and very importantly, there appeared to be a linear and progressive decrease in prostate cancer risk with each additional 30 minutes of walking or bicycling per day over the course of the adult lifetimes of these men (this linear relationship was noted within a range of 30 to 120 minutes of walking or bicycling per day).  Additionally, the risk of developing advanced prostate cancer appeared to be further lessened by regular daily physical activity. 
 
The results of this study mirror those of other high-quality cancer prevention studies for other types of cancer (including, most notably, breast cancer).  While clinical research studies such as this one are prone to various forms of bias, and in particular, biases that arise from patients “self-reporting” their personal health and lifestyle information on study questionnaires, the authors of this study appear to have taken very significant and effective steps to reduce the risk of including such biases in the data that they collected from these nearly 46,000 men.  Therefore, although a small degree of residual error cannot be completely excluded from the results of this impressive epidemiological study, its findings that progressively higher levels of daily physical activity (and, it must be stressed, throughout one’s lifetime) are associated with a decreasing level of prostate cancer risk are very likely to be valid even in the presence of small errors in the study’s data (if they exist).
 
Cardiovascular disease remains the most common cause of premature death in most societies.  Cancer is the number two cause of premature death when including people of all ages, and the number one cause of premature death below the age of 80 in the United States.  Regular exercise, including relatively moderate activities such as brisk walking or bicycling, have been shown to significantly reduce the risk of death due to cardiovascular disease, as well as, increasingly, the risk of developing or dying from multiple different types of cancer.  Based upon the results of this well designed and well executed prospective clinical research study, it would appear that prostate cancer can be added to the list of life-threatening illnesses for which the risk can be decreased through regular and frequent physical activity (and both at work and at home).

Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity