By Dr. Gordon Chang
Safety of the Sunshine Vitamin
Making sense of the opposing studies on vitamin D
In June of this year, the Canadian Cancer Society set an unusual precedent by recommending Canadian adults supplement daily with 1000 IUs of vitamin D, based on their investigation of the scientific research supporting this supplement as a preventative measure against certain forms of cancer. Conversely, the American Cancer Society advised consumers not to supplement with vitamin D, citing that further research needed to be undertaken, yet they admitted that the current daily limit of 200 to 400 IUs for adults was too low. So which Cancer Society is correct?
According to the American Institute of Medicine's Food and Nutrition Board, the acceptable highest level of vitamin D to take is 2000 IUs in adults aged 19 and older. However, the vitamin D that is made and used by the body is closely regulated and therefore vitamin D toxicity usually only occurs if extreme doses are consumed. For example, exposure to sunlight for long periods of time will not cause vitamin D toxicity. This is because the concentration of vitamin D precursors produced in those people with lighter skin colour will reach their healthy balance within about 20 minutes of exposure to UV rays, and any further vitamin D that is produced is downgraded and unused. For darker skinned people it takes about one to two hours for this to occur.
Overdose will occur at more than one hundred times the recommended daily allowance (roughly one bottle of 90 vitamin D tablets per day), and over a period of months. Acute overdose would require taking over 50 milligrams at one time, which is ten thousand times the RDA. Foods contain low levels of vitamin D and have not been known to cause overdose. It is apparent then that vitamin D toxicity is unlikely if consumers take the 1000 IUs daily dose recommended by the Canadian Cancer Society.
What is the best way to obtain vitamin D?
Obviously food is a good source, yet to reach the new proposed RDA of 1000 IUs you would have to consume five times more dairy products (10 glasses of milk daily) and oily fishes such as salmon every day. Short-term exposure to sunlight is crucial, but don’t overdo it due to the risk of skin cancers. If you wish to increase your intake of vitamin D safely when sunlight is scarce, it makes the sense to supplement. Although tablets and capsules are available, a liquid form of vitamin D3 may offer the best absorption.
Why supplement with vitamin D?
Further research on vitamin D is needed, but if current studies show that 1000 IUs daily is safe and helpful for adults then it may be optimal to start now. It has been known for a long time that vitamin D (vitamin D3, or cholecalciferol, the best absorbed type and the form used in the cancer research) is required for calcium absorption, which will aid in overall bone, joint and dental health. Research has also shown that supplementing with vitamin D during winter months or by those who are not often exposed to sunlight can help alleviate the affects of SAD (seasonal affective disorder or “winter depression”).
For those with a genetic predisposition for certain types of cancers such as breast, prostate, skin, lung and colon cancer, there is a benefit to supplementing with vitamin D now instead of waiting for further research. A recent announcement by scientists noted that after reviewing 18 different studies on vitamin D collectively, the research indicated that people would live up to four and a half years longer if they supplemented with vitamin D. This conclusion was drawn by noting that those who did not get enough vitamin D daily were more prone to having their life cut short by illnesses such as cancer, heart disease, diabetes and high blood pressure. Recent evidence also suggests that a higher intake of vitamin D may be helpful in preventing and treating fibromyalgia, multiple sclerosis and rheumatoid arthritis. You should not conclude that vitamin D deficiency is the only cause of these diseases, or that you will not get them if you take vitamin D. But to help prevent these illnesses, vitamin D supplementation could be beneficial.
The benefits are stacking up
In late September of 2007, the Canadian Pediatric Society announced that pregnant women and nursing mothers should talk to their doctors about taking a daily supplement of 2000 IUs of vitamin D. They explained that vitamin D deficiency can lead to serious repercussions in a developing fetus that can be prevented by taking supplements.
A recent study published in The American Journal of Clinical Nutrition fifteen experts from universities, research institutes and university hospitals world-wide called for international agencies to "reassess as a matter of high priority" the dietary recommendations for vitamin D because current information is outdated and puts the public at risk of deficiency (Hyppönen & Power, 2007, p. 860). Interestingly, Health Canada was moved to respond with more caution in their most recent news release regarding vitamin D, warning Canadians “there are health risks associated with taking too much vitamin D and they should not exceed the tolerable upper intake level set for adults at 2000 IUs/day from all sources.”
How much is too much vitamin D?
It seems that the real issue is that Canadians are not obtaining enough vitamin D daily, which may lead to illness and a shortening of life span. After reviewing the scientific evidence relating to vitamin D, Canadian adults would likely benefit greatly from taking 1000 IU of vitamin D daily in addition to their food sources without placing them at any risk of toxicity.
Dr. Gordon Chang
Dr. Gordon Chang holds a Ph.D. in physiology and biomedical engineering from the University of Toronto. He also has two years post-doctoral experience in clinical biochemistry. He currently owns and operates Omega Alpha Pharmaceuticals Inc.
