VITAMIN D & CARDIOVASCULAR HEALTH
The more that we understand about how Vitamin D works in the body, the greater becomes our appreciation of its myriad health-related effects. Previously, this essential vitamin was considered primarily in terms of its important role in the absorption of calcium. (Calcium not only provides strength for our bones, but also plays a critical role as a cofactor in thousands of vital chemical reactions occurring in every cell in our body.) Unique among vitamins, our bodies can actually create Vitamin D as a result of exposure to natural sunlight. However, variations in exposure to sunlight and in skin pigmentation, and in the availability of adequate Vitamin D in our diets, results in wide variations in the level of the active form of Vitamin D in the blood of individuals. Because of these variations, an estimated one-third to one-half of all adults, and especially older adults, have low blood levels of this crucial vitamin.
Two new studies add further scientific evidence strongly suggesting that Vitamin D may also be important in maintaining a healthy cardiovascular system, and in reducing the risk of developing at least some forms of cancer.
In the journal Circulation, researchers from the famed Framingham Heart Study evaluated more than 1,700 adults, with an average age of 59, and without a prior history of cardiovascular disease (except for high blood pressure). During more than 5 years of follow-up, on average, the incidence of cardiovascular events was tracked in these research study volunteers, and these cardiovascular events were then correlated with Vitamin D levels in the blood of the same participants. The cardiovascular events tracked in this study included the new onset of cardiac chest pain (angina), heart attacks, heart failure, strokes, and leg pain due to inadequate blood supply.
During the course of this study, 120 volunteers experienced a new cardiovascular event. Interestingly, study volunteers with high blood pressure appeared to experience significant cardiovascular protection from high levels of Vitamin D in their blood, while patients without hypertension did not. Among the volunteer patients with high blood pressure, those with the lowest levels of Vitamin D in their blood experienced more than twice as many serious cardiovascular events when compared with hypertensive patients who had the highest levels of Vitamin D in their blood.
Recent research has suggested that chronic Vitamin D deficiency may be associated with increased blood pressure, enlargement of the heart, and an increase in the levels of chemicals in the blood that are associated with inflammation. Vitamin D supplementation, in small research trials, appears to be able to improve these adverse effects of Vitamin D deficiency. However, to actually verify that Vitamin D supplementation can reduce the risk of cardiovascular events in patients with high blood pressure, it will be necessary to follow this excellent Framingham Heart Study research trial with another study that randomizes hypertensive, Vitamin-D-deficient volunteers between Vitamin D pills and placebo pills (“sugar pills”). Only then will we be able to clarify the true role of Vitamin D deficiency (and supplementation) in cardiovascular disease and health. Meanwhile, it would seem prudent to make sure that your diet contains adequate daily levels of Vitamin D, and that you avail yourself to reasonable (though not excessive) levels of sun exposure, especially if you have hypertension. (If you are fair-skinned, then please observe the present recommendations regarding safe exposure levels to the sun’s rays.) Of course, please check with your personal physician first, before embarking upon any major changes in diet or dietary supplements, or any other major lifestyle changes.
VITAMIN D & BREAST CANCER RISK
There have been a number of studies suggesting that higher levels of Vitamin D in the blood may be associated with a somewhat decreased risk of developing certain cancers. The data for the possible anti-cancer effects of Vitamin D has been most pronounced for colon and rectal cancer, although not all studies have confirmed this beneficial health effect for Vitamin D. Other studies have also suggested that increased Vitamin D intake may be associated with a modest reduction in the risk of developing breast cancer, as well. Most of these studies, however, have relied upon surveys in which study volunteers have estimated their dietary Vitamin D intake, a method of research that is subject to significant potential inaccuracies. A new study from Germany, just published in the journal Carcinogenesis, has taken a scientific approach similar to the study of Vitamin D’s effect on cardiovascular health that I have just reviewed (above).
In this study, two groups of postmenopausal women, each numbering almost 1.400 in size, were evaluated. One group consisted of women who had been diagnosed with breast cancer between 2002 and 2005, while the second group consisted of age-matched women without a prior history of breast cancer. The level of Vitamin D was measured in all of these study volunteers, and then correlated with the presence or absence of a history of breast cancer.
When comparing the women with the highest blood levels of Vitamin D against the women with the lowest levels, the results were rather striking. Having the highest levels of Vitamin D in the blood was associated with a nearly 70% reduction in the risk of breast cancer, in this population of Northern European women, when compared to similar women with low Vitamin D levels. Because this research study directly measured levels of Vitamin D in the blood, the results are not dependent upon the subjective recollections of study participants. One limitation of this study, however, is that it does not completely prove that Vitamin D deficiency alone is directly causing an increased risk of breast cancer. As I have already mentioned, the absorption of Vitamin D, and the regulation of its level in the blood, are controlled by highly complex biochemical mechanisms. There may be other factors at work that simultaneously increase the risk for breast cancer and decrease the levels of Vitamin D in the blood (i.e., this is the critically important difference between a “cause-and-effect” relationship, on the one hand, and a mere “association” between two unrelated processes or events, on the other hand).
Once again, the next logical step in this area of study would be to perform a new clinical study in which postmenopausal women with low levels of Vitamin D in the blood were randomized between high-dose Vitamin D supplements and placebo pills, and were then followed for at least 5 years. Only this type of study would definitively answer the question of whether of not Vitamin D deficiency, by itself, increases the risk of developing breast cancer after menopause.
GREEN TEA & COLON AND RECTAL CANCER
Much has been written about the potential health benefits of green tea, and especially the antioxidant polyphenols contained within this ancient beverage. As in most areas of cancer research, conflicting results have been published regarding the role of green tea polyphenols as potential cancer prevention aids. Certainly, however, there is ample laboratory data (in cell cultures and in animal models) suggesting that green tea polyphenols may be able to block key mechanisms of cancer cell development.
A new study, also just published in the journal Carcinogenesis, adds to the growing body of data suggesting that green tea polyphenols can indeed block critical cancer-causing biochemical pathways, at least in laboratory rats.
In this research study, laboratory rats were used to assess the effects of green tea polyphenols in the prevention of colorectal cancer. The rats were injected with azoxymethane, a chemical known to induce colon cancer in rats fed a high-fat diet. The rats were divided into 3 groups, with 2 groups receiving green tea dietary supplements (either low-dose or high-dose supplementation), and a third group that received no green tea supplementation in their diet. At the end of the study, the animals were euthanized, and the cells lining their colons were then examined under a microscope for changes consistent with an early transition to colon cancer.
researchers in this study discovered that the rats who received green
tea supplementation had significantly fewer pre-cancerous changes in
the cells lining their colons when compared to the rats that received
no green tea supplementation.
the rats that receive the highest dose of green tea supplementation had
the least number of pre-cancerous changes in colon cells among the 3
groups of rats.
proteins (including beta-catenin and cyclin D1) were also studied in
the colon cells of each group of rats and, once again, the levels of
these proteins were significantly lower in the rats who had consumed
the green tea supplements, and especially in the group of rats that
received the highest dose of green tea polyphenols.
These results strongly suggest that, at least in rats, several key
cancer-associated biochemical reactions can be blocked by green tea
polyphenols, and that microscopic evidence of early pre-cancerous
changes in the cells lining the colon is also reduced by green tea
Unfortunately, countless previous research studies in rats and mice
have failed to show comparably favorable results in humans.
One could imagine a similar study being performed in humans, with the
collection of small biopsies of the colon and rectum performed during
routine screening colonoscopy.
The role of green tea supplements in the prevention of colon and rectal
cancer could then be evaluated objectively in humans.
Meanwhile, I will continue to take my own daily supplements of green
tea in liquid and capsule form.
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.
Dr. Wascher is an oncologic surgeon, professor of surgery, a widely published author, and the Director of the Division of Surgical Oncology at Newark Beth Israel Medical Center
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Copyright 2008. Robert A. Wascher, MD, FACS. All rights reserved.
Dr. Wascher's Archives:1-27-2008: Colorectal Cancer, Esophageal Cancer & Pancreatic Cancer: Update from the 2008 American Society of Clinical Oncology's Gastrointestinal Cancers Symposium
12-16-2007: Honey vs. Dextromethorphan vs. No Treatment for Kids with Night-Time Cough, Acupuncture & Hot Flashes in Women with Breast Cancer, Physical Activity & the Risk of Death, Mediterranean Diet & Mortality