Facts about the Sun as a Source of Vitamin D

In a recent study in the Journal of Internal Medicine, investigators looked at mortality rates of women in Sweden and their sun exposure over a 20-year period, and their findings suggested that women who avoided sun exposure were twice as likely to die compared to those who had sun exposure.

The premise here is that those women who avoided sun had lower vitamin D levels (this is speculation, not fact), and based on epidemiological evidence that links cardiovascular disease and early death among people with low levels of vitamin D, as well as the studies showing that low vitamin D levels have been linked to more aggressive and fatal melanomas, the authors posited that “following sun exposure advice that is very restrictive in countries with low solar intensity might in fact be harmful to women’s health.”

So how to interpret this study, which is making national headlines? Let's look to the limitations to get a feel for its validity:

As noted above, the suggestion that insufficient vitamin D levels among those who avoid sun exposure is the mechanism that raises the mortality rate is only speculation. In their words, “an association,” not causation.
There is no mention or record of vitamin D supplementation use or even the vitamin D levels of participants. In fact, the study looked only at a person’s sun exposure!
The investigators did not distinguish between the associated medical consequences of an unhealthy lifestyle and avoidance of sun exposure.