Hardly a week goes by without some news about vitamin D. While this is gratifying for researchers involved in this area of study, the general public may be more skeptical. Over the years, people have heard many wonderful things about other vitamins, such as E or C, but they often become disappointed to find the excitement soon fades away. Is vitamin D just another flash in the pan? We don’t think so.
Until recently, the fields of nutrition, medicine and public health haven’t taken vitamin D too seriously. Prior to the 1980s, the thinking was that vitamin D was good only for keeping bones healthy, and since men were generally less likely to develop osteoporosis than women, why should they worry? We now know that bone loss also occurs in older men, and this can be a serious concern for those with prostate cancer, both as a result of the disease and due to some treatments.
Not just for bones
We also recognize that vitamin D plays many different roles in the body, not just in strengthening bones. It controls over 60 genes involved in a variety of bodily functions and facilitates communication between cells. A breakdown in communication can result in possible “mistakes” (for example, the development of cancer). This article looks at the biology of vitamin D, its role in health promotion and, possibly, cancer prevention, and provides some specific recommendations for men with prostate cancer.
Our skin: a vitamin D factory
Evolution of any species works by the ongoing selection for characteristics that are most suitable for the environment in which the species develops. In early times, we humans lived near the equator where the full surface of our naked skin was exposed to sunshine year round, so we probably had much higher vitamin D levels than we do now. Humans are the only primates that live in the north, far away from the sun. We can logically ask whether living in a northern climate such as Canada is good for us as a species.
Vitamin D is made when the skin is exposed to sunlight, causing a cholesterol-like molecule called 7-DHC to break open. Some of the oil in and on the skin is absorbed back into the body, where various tissues take it up. Even though a winter day in Canada can be sunny, our skin cannot produce vitamin D if the ultraviolet (UV) index is 3 or less. You can tell if the UV index is 3 when the sun is situated about 45° above the horizon and your shadow is shorter than your height. Another factor in how much vitamin D you make is your age.
We can compensate for lack of sunshine, older age or any other factors that limit our vitamin D level by taking supplements; these work the same as the vitamin D nutrition we get from sunshine.
How much is enough?
A blood test called serum 25 hydroxyvitamin D (25[OH]D) is available to check your vitamin D level. This test has been used extensively to study the role of vitamin D in preventing bone fractures in people with osteoporosis. For most areas of health, studies show that serum 25(OH)D levels should be higher than 75 nmol/L. Unfortunately, many people don’t achieve this desirable amount. For example, Canadians average 25(OH)D levels of 40 nmol/L over the winter, while people who live in sunnier countries often have levels higher than 100 nmol/L.
Table 1 (table see issue pdf http://www.ourvoiceinprostatecancer.com/sites/default/files/OurVoice0404...) lists some conditions (including bone fractures, cardiovascular disease, depression, breast and colon cancer and more) that may be prevented by higher 25(OH)D concentrations. Table 2 (table see issue pdf http://www.ourvoiceinprostatecancer.com/sites/default/files/OurVoice0404...) then narrows in on some important research findings in the field of vitamin D and prostate cancer.
The prostate cancer connection
Canadian research has contributed to the evidence supporting the vitamin D/prostate cancer link. A few years ago, Dr. Richard Choo of Sunnybrook Hospital in Toronto started giving 2,000 IU per day of vitamin D to men with recurrent prostate cancer, based on progressive increases in their prostate specific antigen (PSA) levels. This rather modest dose slowed down the rate at which PSA doubled. Soon afterwards, we wondered if something similar might occur due to the natural summertime dose of vitamin D. A team led by Dr. Laurence Klotz (also at Sunnybrook) had been collecting data from men not diagnosed with prostate cancer but whose PSA levels had been rising between 1995 and 2000 (their PSA was checked every three months). As expected, we found that the increase in PSA, on average, slows down during the summer but continues to increase the rest of the year.
This work helped the National Cancer Institute of Canada justify the funding of a clinical trial, called DProstate, now getting underway in Toronto (for information, see http://clinicaltrials.gov/ct2/show/NCT00741364). This trial doesn’t aim to cure prostate cancer, but rather to explore vitamin D’s effect on prostate tissue when given to men before radical prostatectomy. We expect to show that vitamin D alters the behaviour of cells in the prostate in a “good” (i.e. less cancer-like) way. Similar work has been done in the test tube, but we can’t be sure what happens in humans without this sort of research. Ultimately, clinical studies like this will help determine what vitamin D levels are most beneficial for preventing or managing prostate cancer.
We still have a lot of work to do to understand the connection between vitamin D and prostate cancer, though. In population surveys, 25(OH)D blood test results don’t relate to prostate cancer risk as nicely as they do for cancers of the breast or colon. In the case of prostate cancer, we think the problem may be not so much the low vitamin D level itself but more the highs and lows of the cycle — in other words, the way the vitamin D supply takes big jumps in the summer followed by large drops through the winter. Men with the highest levels of summertime vitamin D also suffer the biggest decreases in winter. In southern latitudes where prostate cancer is less common, men exposed to sunshine all year have steady high 25(OH)D levels.
Recommendations
Until we find out more, it might be wise to ask your doctor about having a vitamin D blood test and taking supplements to correct any deficiencies. Over a year ago, the Canadian Cancer Society suggested that all adults should “consider” taking a 1,000 IU vitamin D supplement daily (rather than issuing a formal recommendation). There are many options for improving your vitamin D intake. Perhaps surprisingly, food isn’t one of them — even a good Canadian diet doesn’t provide the 400 IU/day “officially” recommended for people over age 50 in Canada’s Food Guide. Of note, vitamin D is the only supplement that our Food Guide recommends for adults.
But remember, vitamin D won’t do any good sitting on the kitchen counter or in the medicine cabinet! Adherence is a big problem in the osteoporosis field — even though doctors tell their patients to take vitamin D to prevent bone fractures, less than one-third of patients stick to it for even a year. You’ll find vitamin D supplements in drugstores and health food stores in pill or liquid form. The amount you get in a multivitamin isn’t enough. You should take a dose of 1,000 IU each day, or you can take seven 1,000 IU doses all together, once a week — whatever works best for you. If you miss a couple of doses, combine them to catch up when you remember. The important thing is to keep taking vitamin D on a long-term basis.
Men with prostate cancer or at risk for osteo-porosis may also be advised to take calcium supplements. But since vitamin D increases calcium absorption, adequate vitamin D nutrition may result in less need for calcium. Some calcium supplements include vitamin D in the formulation, although not enough to provide your daily dosage of 1,000 IU. Also, there is debate about the value of calcium intake with prostate cancer. At the very least, stick with the vitamin D by itself if you do not take calcium.
Dr. Reinhold Vieth is Professor in the Department of Laboratory Medicine and Pathobiology, and the Department of Nutritional Sciences at the University of Toronto.
Dennis Wagner, MSc, is a PhD candidate in the Department of Nutritional Sciences, Faculty of Medicine, at the University of Toronto. He is working with Dr. Vieth on a clinical trial examining the effects of vitamin D in men with prostate cancer.
