Scientists and doctors have begun to recognize that almost all of us need to get more vitamin D. Those of us who have diabetes often have very low levels of vitamin D in our systems.
The experts still haven't decided on precisely how much vitamin D we need or the best ways to get it. But two massive new studies have shed much needed light, including a finding that the type of vitamin D that doctors usually prescribe doesn't help at all.
On April 1 the journal of the British Medical Association, BMJ reported two studies that attempted to make sense of the existing data about vitamin D. One of the studies found that people with lower levels of vitamin D in their bodies had a 35 percent greater risk of death from heart disease and a 14 percent greater likelihood of death from cancer. The other study reached a more tentative conclusion that the data shows only suggestive evidence that high levels of vitamin D protect against diabetes, strokes, high blood pressure, and several other illnesses.
An international team, led by researchers at the University of Cambridge and the Erasmus Medical Centre, analyzed the results of 73 observational cohort studies with a total of 849,412 participants and 22 randomized controlled trials with a total of 30,716 participants. The full-text of this study, "Vitamin D and risk of cause specific death," is free online.
The second team, led by researchers in the UK and Stanford University, analyzed 107 systematic literature reviews, 74 meta-analyzes of observational studies, and 87 meta-analyzes of randomized controlled trials. The full-text of this study, "Vitamin D and multiple health outcomes," is also free online.
These studies show that we get vitamin D from five sources:
1. Only a very few foods naturally contain vitamin D. Fatty fish -- like salmon, sardines, and mackerel -- and fish liver oils are the only foods that naturally have more than small amounts.
2. Americans get most of our vitamin D from fortified foods. For example, almost all of our milk includes 100 IU per cup.
3. Almost all of us get at least some vitamin D from exposure to sunlight. While this is the most natural way to get a lot of vitamin D, it has its dangers. And people who live at high latitudes or where cloud cover is high or have dark skin have special challenges in getting enough vitamin D this way. Anyone who uses sunscreens with a sun protection factor of 8 or more is blocking vitamin D, and all of us who get a lot of sun increase our risk of skin cancer.
4. Vitamin D3 supplements are available over-the-counter and are the easiest way to get large amounts of vitamin D in our systems. I have taken at least 5,000 IU daily for several years.
5. Vitamin D2 is typically the supplement form that our doctors prescribe. As recently as 2011 the clinical guideline of the Endocrine Society considered it to be as effective as vitamin D3.
But one of the firmest conclusions and the most striking finding of this new research is that one of these studies found that taking vitamin D2 -- the type that your doctor probably prescribed -- didn't offer any benefit.
By contrast, they found that people taking vitamin D3 had an 11 percent reduction in mortality from all causes compared with people who didn't take it. They calculated that about 13 percent of all deaths in the United States can be due to low levels of vitamin D.
These studies show that we still have a lot to learn. But they also show that having a low level of vitamin D in our system is a risk that we don't have to take.