It is common knowledge that Vitamin D is important for strong bones. We have heard this since we were kids. Drink your milk, it’s fortified with Vitamin D! But the past few years has witnessed an outpouring of new information and new claims for Vitamin D such as: “it will boost your immune system” and “it can help prevent cancer” and the universal “most Americans are Vitamin D deficient."
Vitamin D is Big Business.
In 2008, consumers bought $235 million worth of vitamin D supplements, up from $40 million in 2001. Some experts, though, are starting to sound alarms about the boom in testing, which has been increasing by 80 to 90 percent per year, with several million people expected to be checked in 2010.
Here are some useful facts about Vitamin D. Once you know the facts, you may not be surprised to learn that (oh my!) there has been a lot of hype about this essential but unfortunately, not miraculous vitamin.
What exactly is Vitamin D?
There are 2 forms of Vitamin D in the body. Vitamin D2 (called ergocalciferol) and Vitamin D3 (called cholecalciferol). Both of these forms still have to be converted by the liver into the biologically active form, called calcitriol. Direct sun exposure to our skin enables humans to produce Vitamin D3 (not D2).
How do we measure Vitamin D in the blood?
In the blood we test for a form of Vitamin D called calcidiol (also called 25-hydroxy Vitamin D). Calcidiol is converted into calcitriol, the active form of Vitamin D (also called 1,25-hydroxy Vitamin D). Levels are reported as nanograms per milliliter (ng/ml). The normal range varies depending on the lab. Low Vitamin D might be less than (<) 18 ng/ml in one lab or < 30 ng/ml in another lab.
What does Vitamin D actually do in the body?
Vitamin D is necessary for the body to be able to absorb calcium in the intestines. It is also needed to help regulate the blood levels of calcium and phosphorous in the body. A deficiency of Vitamin D causes rickets; a disease characterized by extremely soft bones and bent legs. In the U.S. this is a rare disease, but it's not so rare in poorer countries.
What is the daily dose of Vitamin D supposed to be?
The recommended daily dose of Vitamin D is 400-600 units (higher for the elderly and lower under age 1). High doses can lead to toxicity, characterized by nausea, vomiting and hypercalcemia (elevated calcium in the blood that can cause seizures and kidney stones). Doses of 1,000 units per day given to an infant can lead to toxicity in 1 month. Units are also called IU for International Units.
Sun-exposure Vitamin D production
If you're fair skinned, experts say going outside for 10 minutes in the midday sun -- in shorts and a tank top with no sunscreen -- will give you enough radiation to produce about 10,000 IU of the vitamin. But in winter there is not enough UV-B radiation for most people to produce Vitamin D, even with good sun exposure.
Naturally occurring Vitamin D
A great source of both Vitamins A and D is cod liver oil (1 Tbsp. contains 1,400 units!). Fish such as salmon, catfish, sardines and tuna are rich sources, providing about 300 units of Vitamin D per 3 oz. portion. Interestingly, a quart of milk provides only 400 units of D. Human breast milk is naturally quite low in Vitamin D. Also, almost no vegetables, fruits or nuts contain Vitamin D (small amounts are in mushrooms).
Can Vitamin D prevent cancer?
Many studies have looked at this. Vitamin companies heavily promote this and advise people to take high doses, 1,000 to 2,000 units a day, to try and prevent cancer. The boring truth…there is no proven cancer protection benefit from high Vitamin D, and there IS a proven risk.
What are the other supposed benefits of Vitamin D?
Some studies showed a lower risk of dying from cancer, any kind of cancer. Some showed a boost to the normal immune system, and a lower risk of getting the flu. Others show reduced risk of diabetes and heart disease and high blood pressure. None of these studies are considered proof.
What is proven about Vitamin D?
When Vitamin D supplements were given to elderly nursing home residents, along with a calcium supplement, there were fewer bone fractures in the treated group. Vitamin D and calcium can help prevent osteoporosis, likely due to fixing a deficiency, rather than any benefit from megadoses.
A team of scientists at Boston University School of Medicine, determined that topical Vitamin D could be used for the treatment of psoriasis. Initial experiments with vitamin D hormone have shown that topical applications of the hormone are remarkably effective. In 1994 the U.S. Food and Drug Administration approved a vitamin D-based topical treatment for psoriasis, called calcipotriol (Dovobet).
The promising benefits of high vitamin D amounts were demonstrated in studies that simply looked at vitamin D levels in various populations and then correlated them with disease. But, people need to realize that high levels of vitamin D in the bloodstream may just be due to good genes or some other factor beyond sun exposure or dietary intake. This is not proof of any beneficial effect.
Experts advise us not to “...jump on the bandwagon and take megadoses before we have results from research trials.” After all, a host of supplement studies—on vitamin C, vitamin E, selenium, beta carotene—found that those who were given supplements fared no better, and sometimes worse, than those who took placebos.
Yes, we all need adequate Vitamin D intake, but the evidence for additional health benefits from taking high doses is just not there. Food can provide enough Vitamin D but supplements work just as well and vegans have to take supplements. Milk is actually a poor source of Vitamin D because very few people will drink one quart of milk per day to get their 400 units! Be wary of the "emergency" need to supplement with 50,000 units of D just because your blood level is below 30 ng/ml. Many experts believe that levels above 18 ng/ml should be considered normal.