Recent research on vitamin D and its relationship to decreased cancer rates led to a recommendation in June 2007 from the Canadian Cancer Society that adults should consider increasing their daily dosage of vitamin D. The suggested amount, at least for fall and winter months, is 1,000 international units (IU) daily.
According to Dr. Christopher Kovacs, an endocrinologist in the Faculty of Medicine, the average person should be supplementing their diet with at least that amount of vitamin D, if not more.
“There’s a lot of evidence that we’re generally not taking enough vitamin D. Normally it’s produced by the interaction of skin and sunlight but in the modern age of sunscreen lotion and hats, we’re not producing it naturally,” he said. “If you were outside in sun all day without protection, your body would be making between 10 and 20,000 international units a day of vitamin D.”
The National Institutes of Health is holding a consensus conference Sept. 5-6 in Bethesda, Md., to determine the current state of knowledge about vitamin D, where the knowledge gaps are, and to identify the research priorities for the future. Dr. Kovacs is one of 20 international experts on vitamin D who have been assembled to speak at this conference. His topic is vitamin D in pregnancy and lactation.
The major function of vitamin D in the body is to maintain normal blood levels of calcium and phosphorus. By promoting calcium absorption, vitamin D helps to form and maintain strong bones. Dr. Kovacs describes the story of how current vitamin D recommendations came about as horrifying.
“With very severe vitamin D deficiency there’s a condition called rickets in children or osteomalacia in adults. In children, this means their bones are very soft and become deformed at an early age.
“Back in the early 1900s, it was recognized that a teaspoon of cod liver oil would prevent rickets. So-called experts got together and decided that if a teaspoon works in an infant than an adult probably needs half that but it makes much more sense that, based on body size alone, an adult should need more vitamin D than a small infant!”
When it was discovered that vitamin D was the active ingredient in cod liver oil, the amount worked out to be about 400 IU in a teaspoon. “So the recommendations were just sort of transferred to say that infants and children needed about 400 IU of vitamin D and adults 200 IU,” said Dr. Kovacs. “It was also decided about 30 years ago that five times that amount (1,000 IU per day) is potentially toxic as part of expert opinion hocus-pocus that was held up with no science behind it.”
Until recently, the focus on vitamin D was its role on the skeleton.
“We understood that vitamin D gets converted through a series of steps to an active hormone that stimulates the absorption of calcium by the intestine. If you don’t have enough vitamin D you can’t maintain the necessary mineral content of your skeleton and your body starts stripping the skeleton to maintain the daily need for calcium, and that can result in an early form of osteoporosis.”
Dr. Kovacs explained that original studies measuring vitamin D in the blood were based on population averages.
“But like weight, the average is not the healthiest. For the population in this province we redefined the normal value of vitamin D to agree with the international standards for the level of vitamin D that are associated with normal bone, muscle and neurological function. We’re now finding that 90 per cent or more of people tested have low levels. For those people, 1,000 IU supplementation a day will bring 75 per cent into a normal range and 2,000 IU supplementation will bring 90 per cent to a normal range.”
One caution with taking vitamin D as a supplement is to take it with the largest meal of the day. Because it is a fat soluble vitamin it is not absorbed well if it is taken first thing in the morning or between meals.
In terms of preventing cancer, Dr. Kovacs said that the immune system is impaired by low vitamin D.
“By supplementing with vitamin D you are probably boosting the immune system, which helps to fight cancer. There is other evidence that shows it affects immune-related diseases such as type 1 diabetes and multiple sclerosis.”
With type 1 diabetes, Dr. Kovacs said a number of studies have shown that if the mother’s vitamin D status is low, their children are more likely to develop type 1 diabetes.
“Vitamin D crosses the placenta so the baby ends up at birth with the vitamin D levels the mother had. If the mother’s levels are low, the baby will be born with low levels.”
Is there a downside to supplementing with vitamin D? Dr. Kovacs cautions that it is not a magic bullet, but is generally beneficial for most people. However, for those with a history of kidney stones, it can raise the risk for developing more stones. “Anyone with a history of kidney stones should be investigated by a physician first before taking vitamin D.”
Is there a toxic amount of vitamin D? It’s rare, but Dr. Kovacs has seen a few people with levels so high they couldn’t be measured.
“It usually happens if they were prescribed a 50,000 IU supplement to be taken once every two weeks and they misunderstood and took it daily. The important thing to remember is that your body would normally produce 10,000 IU of vitamin D from daily sun exposure, so if you are not getting that exposure it is very difficult to take too much vitamin D in the form of a supplement.”