Rock Doc

My scientific training tells me that the days are getting a little bit

longer now. And I do believe that. But my spirits say it remains dark

awfully long into the morning and the sun surely sets early in the

afternoon.

Even if you aren’t affected emotionally by the short days of winter,

could they affect your health? That depends on whether low levels of

vitamin D in the body are bad for you.

One way we get vitamin D is by manufacturing it in our bodies when

sunlight strikes our skin. In the winter, not only are the days short,

but we often are covered up for warmth, making the manufacture of

vitamin D fall considerably from summer values.

Doctors have struggled for some time over the question of whether a low

vitamin D level in the blood causes disease or whether poor health is

the cause of low vitamin D values. A recent study in Europe makes the

case that a low level of the vitamin is, itself, a factor that increases

the death rate. The study used a technique called Mendelian

randomization to pick apart what was causing what in a large data set.

Shoaib Afzal of Copenhagen University Hospital was the lead author of

the study recently published in the journal BMJ. The research used

information from over 95,000 people in Denmark. The entire group was

tested for a natural genetic condition that reduces vitamin D in the

body. Over 35,000 people in the group also had their serum levels of

vitamin D measured. Using medical records, the researchers knew 10,349

of the people in the group died from 1981 to 2013.

The study hinges on the fact that it had two large sets of people to

study: one that had the genetic condition for low vitamin D and the

other that did not. The researchers assumed that so-called confounding

factors, like cigarette smoking, obesity, diabetes, etc., were similar

in the two groups. In other words, the only difference between the two

large groups was the genetic condition and its associated impact on

vitamin D levels.

The researchers found that having the genetic variant, and hence low

vitamin D levels, increased the risk of death by some 30 percent. It

increased the risk of death due to cancer by more than 40 percent.

Interestingly, it had no effect on death caused by cardiovascular disease.

When it comes to vitamin D levels and death, “this study shows there may

be a causal relationship,” Afzal was quoted as saying to The New York

Times. But more work must be done before Afzal’s team would recommend

you take vitamin D tablets.

There are some gray areas when it comes to Vitamin D, just like the gray

weather common this time of year. Ask your doctor if you should be

tested for Vitamin D levels or what her opinion is about the risks

versus the benefits of supplements.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a

geologist at Princeton and Harvard. This column is a service of the

College of Agricultural, Human, and Natural Resource Sciences at

Washington State University.