What's up with D? Understanding the sunshine vitamin

Fred Hutch researchers help you understand what you need to know about the sunshine vitamin
Vitamin D
Illustration by Kim Carney

You might say vitamin D is having its day in the sun.

Earlier this month, two big studies published in the British Medical Journal pointed to a potential link between insufficient levels of the sunshine vitamin and cancer, heart disease and other illnesses. Another study, published in March, found that higher vitamin D levels were associated with lower breast cancer mortality rate.

Now, a new Fred Hutchinson Cancer Research Center study published online Friday in the American Journal of Clinical Nutrition, has found that healthy or “replete” levels of vitamin D may be associated with weight loss – at least in a certain segment of postmenopausal overweight women.

Breast cancer, heart disease and weight loss make up quite the formidable trifecta. Is D really that big of a deal?

What’s the deal with D?

“Vitamin D is certainly having its day in the spotlight and is very ‘trendy’ right now,” said Dr. Caitlin Mason, one of the researchers who worked on the Hutch’s vitamin D and weight loss study. “But we still have a lot to understand.”

Dr. Caitlin Mason
Dr. Caitlin Mason in her office at the Fred Hutchinson Cancer Research Center on April 19, 2014 Robert Hood / Fred Hutch

What does seem clear is that maintaining a healthy level of vitamin D is crucial to human biology and good health. The problem, researchers say, is that people don’t think about getting their vitamin D levels checked the same way they do cholesterol levels or blood pressure.

And they definitely should.

“Vitamin D is something people are really familiar with,” said Mason. “You can stroll down the aisle at the drugstore and get it. But there are dangers with it being too low or too high. It’s best to talk to your doctor about getting tested so that any supplementation you take is really personalized. That’s the biggest take-home message.”

Hidden benefits of D

In the past, most of the research on D has been focused on bone health due to its role in calcium absorption. More recently, however, the focus has switched from bone health to vitamin D’s effect on cardiovascular health, cancer outcomes, and other areas, such as weight loss.

The recent Fred Hutch study – conducted under the auspices of the larger Vitamin D, Diet and Activity (ViDA) study -- looked at the results of D3 supplementation on a group of overweight women ages 50 to 75 who tested low in D.

According to Dr. Anne McTiernan, principal investigator of the study, women whose vitamin D levels rose to what is considered a healthy level lost more weight, body fat and waist circumference than women whose levels did not become replete or who were assigned placebo.

These “replete” women lost an average of 19 pounds over the course of 12 months as compared to the women in the placebo group, who lost an average of 12 pounds during the same time period. Both groups participated in a reduced-calorie diet and an exercise program that included approximately 45 minutes of moderate-to-vigorous aerobic activity five times a week.

“This suggests women trying to lose weight might want to have their D levels checked by their provider and replenish their vitamin D levels either through supplements or sun and then have their D levels rechecked after a few months to make sure they’ve risen to a healthy level,” said McTiernan.

Vitamin D and inflammation

While the weight loss results weren’t overwhelming (“vitamin D is not a magical supplement for that,” said Mason), fellow researcher Dr. Catherine Duggan points to an additional boon. Women in the study who took most of their vitamin D medications showed a drop in an inflammation protein called C-reactive protein.

“An overweight person’s body is in a state of chronic inflammation, and all of these inflammation proteins that the body produces can cause things like elevated risk for cancer and diabetes,” she said. “Vitamin D helped with that. It could make the condition of being overweight less stressful [on the body].”

It’s now known that fat tissue is “like an extra organ” pumping out proteins that cause inflammation, said Duggan. “That can lead to developing diabetes, cancer and a variety of other conditions.”

Fred Hutch’s Dr. Mario Kratz is currently researching vitamin D’s role in managing what’s come to be known as adipose tissue inflammation. He recently conducted a pilot study on the subject; a more comprehensive study is in the works.

Mason said, “One of the prevailing theories is that vitamin D – a fat soluble vitamin – is stored in adipose tissue and therefore people with more fat tissue store away more vitamin D, making it less available in their blood. That may be one reason why they have lower blood levels.  We do know that when a large amount of weight is lost by diet and exercise, there’s more D available in the blood stream. However, this effect is still fairly modest relative to the change that can be achieved through appropriate supplementation.”

Vitamin D needs to be circulating in the blood to be available to the body and used for a number of physiological processes, which may include reducing inflammation.

Further studies are needed, she said, to understand exactly how D is metabolized in fat tissue.

What’s normal?

The National Institutes of Health’s current recommended daily allowance for men, women and children age 1 year and older is 600IU, but Mason said there’s still debate over what optimal levels of vitamin D are.

The best indicator of D status is blood concentration of 25-hydroxyvitamin D. The NIH lists 25 (OH) D levels of less than 12 ng/mL as deficient, associated with rickets in children and osteomalacia in adults. Twelve to 20 ng/mL is considered inadequate for bone and overall health in healthy individuals. More than 20 ng/mL is considered adequate.

While the NIH lists anything over 50 ng/mL as too high, others in the scientific community consider anything between 30 ng/mL and 80 ng/mL as normal. In the weight loss study, women were considered replete at around 32 ng/mL.

People do absorb vitamin D differently, Mason also pointed out, depending on their age, body weight, sun exposure, skin pigmentation and other factors. And certain medications – including those for high cholesterol, high blood pressure and hormone replacement – can interfere with vitamin D metabolism.

Relying on the sun for vitamin D is also tricky, especially for people with a history of skin cancer or who live in cloudier climes, like Seattle.

See your doc

A simple blood test can quickly determine whether a person’s vitamin D level is low, high or in that Goldilocks zone of “just right,” but Mason said many people opt to blithely self-medicate with supplements instead.

And despite all the promising research surrounding vitamin D, that too can be risky. Too much D can lead to abnormally high blood calcium levels, resulting in everything from constipation to kidney stones.

“Your over-the-counter pain medications come with a warning about what’s too much, but unfortunately vitamin D doesn’t,” she said. “Very few people realize that high levels can be toxic.”

Her advice?

“It’s worth at least having a conversation with your doctor about getting tested,” she said. “People can take the same amount of supplementation and have different responses in their blood. The only way to know for sure is to get it checked by your doctor.”

Diane Mapes is a staff writer at Fred Hutchinson Cancer Research Center. She has also written extensively about health issues for nbcnews.com, TODAY.com, CNN.com, MSN.com, Columns and several other publications. She also writes the breast cancer blog, doublewhammied.com. Reach her at dmapes@fredhutch.org.

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