Back in March I discussed an ad campaign sponsored by the Indoor Tanning Association promoting the supposed health benefits of tanning. Their message, in part, touted the benefits of Vitamin D, which is made in your body in a multi-step process that begins with exposure of your skin to ultraviolet light. I argued that with vitamin fortification of foods, vitamin D deficiency was rare in this country. One of my readers astutely pointed out that low vitamin D levels can cause problems even in patients who do not have an absolute deficiency.
A recent study from Mount Sinai Hospital in Toronto supports this idea. The researchers measured vitamin D levels in the blood of 512 women at the time of their breast cancer diagnosis (between 1989 and 1995). In 2006, distant disease-free survival (the percentage of women alive with no evidence of spread of their disease) was 83% for the women with adequate vitamin D levels, compared with 79% for those with insufficient levels and 69% for those who were deficient.
Considering the large number of women diagnosed with breast cancer each year, these differences are huge.
What does this mean? It means a healthy level of vitamin D is probably important for a lot more than just maintaining strong bones.
It is important to note, though, that this study does NOT show that vitamin D helps treat breast cancer, so if you already have breast cancer, supplementation may not help. Also, the study showed that the women with the very highest vitamin D levels seemed to have worse survival, so mega-doses of vitamin D may not be such a good idea, either.
So how much is enough? That varies with age, gender, and whether you are pregnant or nursing a baby. As a general rule of thumb, between 400-600 international units (IU) appears to be a healthy amount. For your specific case, you can consult the Vitamin D Fact Sheet from the Office of Dietary Supplements of the National Institutes of Health here.
Where do you get vitamin D? Your body will make it as long as you get some sun – experts recommend 15 minutes or so a few times a week (without sunscreen, so longer if you have sunscreen on) – but this will depend on where you live (the sun is stronger the closer you are to the equator). Some foods naturally contain vitamin D, like fish (especially salmon, tuna, and mackerel), beef liver, and egg yolks. The major source of dietary vitamin D in the US is fortified dairy foods.
This study was released in advance of the 2008 annual meeting of the American Society of Clinical Oncology (ASCO), which will be held at the end of the month in Chicago. The study has gotten a lot of media attention so far and as I will be at ASCO I will share what I learn.
Check out the study abstract here.