Today’s Boston Globe has an article about a study from Children’s Hospital in Boston that explores the high rate of insufficient vitamin D in otherwise healthy infants and toddlers. (12% deficient in vitamin D and 40% with suboptimal levels.) The study also noted that one-third of these children with low levels of vitamin D had pathological bone changes seen on x-rays.

What Does Vitamin D Do?
What the research study did not examine – but the Globe story does mention – is that in recent years there has been extensive investigation and speculation about the role of vitamin D plays in many other areas of health besides strong bones and teeth. For example, the NIH’s Vitamin D Fact Sheet notes that vitamin D may play a role in lowering the risks of certain cancers:

Laboratory and animal evidence as well as epidemiologic data suggest that vitamin D status could affect cancer risk. Strong biological and mechanistic bases indicate that vitamin D plays a role in the prevention of colon, prostate, and breast cancers. Emerging epidemiologic data suggest that vitamin D has a protective effect against colon cancer, but the data are not as strong for a protective effect against prostate and breast cancer, and are variable for cancers at other sites. Studies do not consistently show a protective effect or no effect, however. One study of Finnish smokers, for example, found that subjects in the highest quintile of baseline vitamin D status have a three-fold higher risk of developing pancreatic cancer.

The NIH’s Fact Sheet goes on to note that vitamin D may play a role in preventing diabetes, high blood pressure and multiple sclerosis. A July 2007 review article by Dr. Holick in the New England Journal of Medicine expands upon this information:

The discovery that most tissues and cells in the body have a vitamin D receptor and that several possess the enzymatic machinery to convert the primary circulating form of vitamin D, 25-hydroxyvitamin D, to the active form, 1,25-dihydroxyvitamin D, has provided new insights into the function of this vitamin. Of great interest is the role it can play in decreasing the risk of many chronic illnesses, including common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease.

The fact that vitamin D plays more than one function in the body should not be surprising, since many physiologically compounds serve multiple functions – from neurotransmitters that act in both the GI and CNS systems, to proteins whose breakdown products also have cellular activity. What this points out is that people (and all animals) are not simple biological systems. While I’ll leave a discussion of the exploding field of systems biology for another time, I do want to point out that once we “know” something in medicine it usually means “what we know right now.” As a professor in medical school said “Half of what we’re going to teach you is wrong, we just don’t know which half.” (I think every medical student gets this in some lecture – it must be in the “Medical School Professor’s Crib Notes.”)

So How Much Vitamin D?
This evolving scientific certainty brings us to the question of how much vitamin D people should be getting – and by what route. There is still no academic agreement as to how much vitamin D people should have – although individual needs do depend upon age, gender, skin color, and medical condition (including pregnancy). But there is a growing consensus that most people need more Vitamin D than they are getting.

The three basic routes for getting more vitamin D are supplements, diet, and sun exposure: The latter is somewhat problematic as the rising incidence of skin cancers places greater emphasis on using sunscreen. Supplements are great – particularly for time limited use in select populations like infants who are breast fed. (That was a risk factor in the Children’s Hospital study.) This leaves us with food.

While milk has long been supplemented with vitamin D, milk consumption in adults is very variable – so more foods are being supplemented. Because vitamin D is much more effective when consumed with calcium, vitamin D is increasingly being added to fortified juices, cereals, and now yogurts. In fact, last year, after seeing several articles about the expanding importance of vitamin D (including the NEJM review article) I called Stonyfield Farms to ask why their yogurt didn’t have vitamin D added to it – as did some of their competitors. The person I talked to was very nice, but didn’t have a very convincing answer. However, I recently noticed that Stonyfield yogurts now have added vitamin D. After making this discovery, I found their October 2007 “Moos From The Farm” newsletter that discussed their plans for adding vitamin D to their products over the winter:

Vitamin D in Our Fat Free
When we converted our fat free yogurts to organic on the 1st of this month, we also added vitamin D, which offers a bunch of important health benefits. Vitamin D…

• increases calcium and phosphorous absorption, which decreases the risk of osteoporosis;
• has immune-boosting properties;
• may help to reduce 17 different types of cancer;
• may decrease the incidence of multiple sclerosis;
• helps to maintain optimal muscle strength;
• benefits diabetics and those with hypertension.

We’ll be adding vitamin D to more of our yogurts this winter, so stay tuned!

I would be tempted to say that Stonyfield added the vitamin D as a marketing pitch, but I haven’t seen any ads or labeling changes that now tout, “Now Healthier – With Added Vitamin D!!!,” so I think they did it because it was a good thing to do, they saw the trend towards a greater emphasis on consuming more vitamin D and wanted to be ahead of the movement – and maybe, possibly, perhaps because I called last summer and asked the question.

So while the optimal level of vitamin D consumption is uncertain, taking too much through food seems hard to do. The NIH’s Fact Sheet notes that there doesn’t seem to be any risk of toxicity from too much vitamin D until you get above 2,000 International Units (IUs) per day, and Holick’s NEJM review states that toxicity doesn’t start until you reach 10,000 IU/day. And as the NIH Fact Sheet notes, “High intakes of dietary vitamin D are very unlikely to result in toxicity unless large amounts of cod liver oil* are consumed; toxicity is more likely to occur from high intakes of supplements.” [*Cod liver oil has 1360 IU per tablespoon.]

Talk With Your Doctor and Summertime Eating
So when you’re deciding about what you’re going to eat – or you’re talking with your doctor and other healthcare professionals about diet and its impact on disease risks – think a bit more about vitamin D and how much you’re getting. This is particularly true for people with some medical problems, risks, or who are taking certain medications that can interfere with vitamin D’s actions or calcium absorption. But also remember, while increased sun exposure increases your vitamin D, ice cream – although great in the summertime – unfortunately it’s not a great source of vitamin D, and it has lots of fat and calories. So think of it as a treat and not a vitamin D supplement….. Or maybe just think of it as a “supplemental treat.”

A friend wearing a t-shirt from our favorite dairy on a very cloudy day at the beach.