The Link Between Weight and Vitamin D

Does a lack of vitamin D bring on obesity?

With Craig Primack MD, Elena Christofides MD, and Megan M. Knuth PhD

Vitamin D

"People ask all the time about vitamin D,'' says Craig Primack MD, an obesity medicine physician, co-founder of the Scottsdale Weight Loss Center, and president of the Obesity Medicine Association. "We know obesity leads to deficiency in vitamin D. But does it cause it? In humans we have never shown that."

However, he adds, "I don't think obesity is one disease.'' He speculates, "There may be a subset of people who have vitamin D deficiency. Low vitamin D may be leading to the obesity, or genetic factors may lead to both the deficiency and obesity."

Elena Christofides MD, FACE, and CEO of Endocrinology Associates in Columbus, Ohio, tells her patients, ''Vitamin D is the most crucial hormone the body makes. It regulates endocrine, immunologic, and metabolic functions."

Obesity is associated with vitamin D deficiency, says Christofides, an editorial board member of Endocrine Web."But, ultimately, most studies looking at vitamin D and obesity are not conclusive," she says. 

What's accepted about vitamin D: It promotes the absorption of calcium in the gut and helps maintain adequate levels of calcium in the blood so that bones stay healthy. It also helps reduce inflammation and modulates cell growth and immune function.

Still unfolding is the debate about vitamin D and obesity. Many researchers have reported that obese people tend to be low in vitamin D. As a fat-soluble vitamin, it has been suggested that it may end up trapped in fat cells.

But some researchers wonder if the deficiency in vitamin D actually comes first. The scientists who most recently tested the theory that the deficiency comes first studied the link between vitamin D and fat in zebra fish. 

Details of the new study

A team of researchers from North Carolina State University used the zebrafish model to determine which comes first, deficiency in vitamin D or obesity. They put the fish on one of three diets—no vitamin D at all, vitamin D enriched, or a standard laboratory diet. The researchers evaluated the growth, bone density, and vitamin D levels of the zebra fish over time.

Zebra fish in the deficient group were about 50% smaller than those in the other two groups and had more fat reserves. They had an increase in both the size and number of fat cells. As a result, the researchers concluded that vitamin D plays an important role in channeling energy into growth instead of fat storage.

Next, the researches gave the deficient fish a vitamin D enriched diet for 6 months to see if the results could be reversed. The fish never caught up in size with the other group and kept their fat deposits.

The researchers had received similar results when they knocked out the vitamin D receptor in the fish, says Megan M. Knuth PhD, one of the study authors. "But this is the first time a dietary approach has been taken."

Human studies

Over the years, researchers have published numerous studies on the relationship between vitamin D levels and obesity in human subjects, including the following:

  • Researchers evaluated data from more than 42,000 people and gave them scores based on their gene variants that affect weight and how they break down vitamin D.  They found that a higher BMI leads to a lower vitamin D status, but the effect of low vitamin D status on weight is likely to be small. Their findings support evidence for obesity leading to vitamin D deficiency, but not vitamin D deficiency causing obesity.
  • Another study, published in 2019, concluded that low vitamin D could not yet be excluded as a cause of obesity, due to a lack of complete research.  

Expert perspectives on vitamin D

It's difficult to get enough vitamin D, which is produced when ultraviolet rays from sunlight strike the skin and trigger vitamin synthesis. Few foods contain vitamin D naturally. Among the best sources are the flesh of fatty fish such as salmon, trout, tuna, and mackerel.

How much is enough vitamin D for patients to take each day? An adequate intake of vitamin D for adults 19 to 70 is 600 international units (IUs) daily, and 800 IUs for those 70 and older. The upper safe limit for adults is 4,000 IUs a day, according to the Institute of Medicine. A vitamin D blood level of 50 nmol/L or higher is generally considered adequate for bone and overall health, according to federal guidelines.

But those numbers are being called into question. "The normal levels of vitamin D that are recommended in the US are the bare minimum necessary to avoid rickets," Dr. Christofides says. "That was the original criterion used to determine what was normal.''

Christofides suggests that a range of 65-85nmol/L is a better goal to advise patients to aim for. "I advise all of my patients to take enough vitamin D to raise their levels to between 65-85."

Individual evaluations are needed, agree Dr. Christofides and Dr. Primack. Both advise a blood test to measure vitamin D levels and provide a starting point as to how much a patient should take. Primack often prescribes 1,000 IUs a day to some patients, or even more, depending on the blood test results and their health.  

Some people need a ''kick-start" dose of 50,000 IU's a week for 4-8 weeks, then can transition to lower doses, Dr. Primack says.

Once patients are prescribed a vitamin D supplement, they often ask Dr. Primack, "If I normalize my vitamin D, will it help in my weight loss efforts?"

He tells his patients, "Not directly." But having enough vitamin D circulating may help people feel better, sleep better, and have more energy, which may translate to being more active and losing weight, he says.

Dr. Christofides reports grants or research support from Pfizer, GlaxoSmithKline, Janssen, Sanofi-Aventis, Novo Nordisk, Lexicon; consultant work for Novo Nordisk, Eli Lilly, Chiasma; speakers' bureau for Pfizer; Novo Nordisk, Eli Lilly, Boehringer Ingelheim, PamLab, and Shire.

Continue Reading:
Can Vitamin D Help Control Weight and Blood Glucose?
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