Low Vitamin D Concerns Lead to Overtesting and Overtreatment

Marcia Frellick

March 04, 2017

ORLANDO — If there's any question you're not getting enough vitamin D from incidental sun exposure and diet, take a supplement, said Barbara A. Gilchrest, MD, here at the American Academy of Dermatology Annual Meeting.

"This preoccupation with vitamin D status has led to an enormous amount of testing, which is expensive and not as reliable or consistent as we might like," said Dr Gilchrest, a dermatologist with Massachusetts General Hospital in Boston.

"If everybody just took one supplement a day, [the tests] would be unnecessary," she explained.

But for most patients, she added, sun and diet should be enough.

Dr Gilchrest also said there is much confusion surrounding the measurement of vitamin D. Some clinicians incorrectly interpret 20 ng/mL — recommended by the Institute of Medicine — as a 25-hydroxy vitamin D test cutoff under which people aren't getting enough of the vitamin.

"What that means is that if you have a level of 20 ng/mL, you have a 97.5% chance that you're getting all the vitamin D you need," she explained. But "for many people, 16 or 12 ng/mL is adequate. Half the population is believed to have totally adequate vitamin D at a level of 16 ng/mL."

 
Half the population is believed to have totally adequate vitamin D at a level of 16 ng/mL.
 

Susan Roper, MD, a dermatologist with Countryside Dermatology and Laser Center in Clearwater, Florida, said that her patients — most of them elderly — have suffered when tests have misleadingly shown their Vitamin D levels are low.

Elderly patients, with thinning skin, have low vitamin D levels to begin with, she explained, and because of fasting before testing, any effects of supplementation are no longer in their systems. This triggers some physicians to prescribe high doses, she said.

"They're put on toxic levels of vitamin D, sometimes 4000 to 10,000 IU a day," she told Medscape Medical News. "A lot of my patients already have arthritis, and that high level of vitamin D makes it worse."

Intentional UV Exposure

Dr Gilchrest also addressed what she calls a "pseudo controversy" perpetrated by advocates of intentional UV exposure, including indoor tanning companies, as a means to maximize vitamin D levels to prevent diseases, including some cancers, diabetes, and multiple sclerosis (MS).

"This is irrational," she said, "because ample vitamin D can be obtained from the diet, supplements, and incidental sun exposure, including incidental, protected sun exposure. And a supplement of 1000 IU/ day for adults is safe and sufficient."

She gave the example of a fair-skinned teen who wants to maximize vitamin D photosynthesis to avoid diseases associated with vitamin D deficiency, such as colon or breast cancer, later in life.

The scenario assumes the minimal erythemal dose is 15 minutes of sun exposure. Maximum vitamin D production will be achieved in 5 minutes, said Dr Gilchrest.

Assuming a 30 SPF sunscreen is applied at 1 mg/cm2 (the thin coat most people apply), which yields an actual SPF of about 5 before a 30-minute sun exposure, the teen "would have no sunburn and an approximately 80% reduction in photo/DNA damage, and maximum vitamin D synthesis," she explained.

"With no sunscreen she would have a painful sunburn, substantial photodamage, and increased skin cancer risk — and the same vitamin D synthesis."

Association, Not Causation

Henry W. Lim, MD, chair emeritus of the Henry Ford Hospital in Detroit, Michigan, discussed the controversies surrounding the literature linking vitamin D levels to certain diseases.

"The association between vitamin D and bone health is indisputable," he said. "That is a cause-and-effect relationship."

The controversy lies in some other links that are associations but have not been found to be causative, said Dr Lim.

He used the example of MS, citing early data from a US military personnel study (JAMA. 2006;296:2832-2838) which showed the risk of MS significantly decreased with increasing vitamin D levels in the blood.

He also cited data from 321 peer-reviewed studies (J Neurol Neurosurg Psychiatry. 2011;82:1132-1141) which showed that globally, the less sun exposure one gets, the greater the probability of developing MS.

In addition, low blood levels of vitamin D were associated with increased activity and progression of MS in a study from China (J Neuroimmunol. 2016;297:127-131), and vitamin D supplementation decreased the annual relapse rate of patients with MS in a study from Denmark (Mult Scler Relat Disord. 2016;10:169-173).

"So there are a lot of data suggesting there could be an association," Dr Lim told the audience, "but I want to emphasize there is no indication for a cause-and-effect relationship as yet."

Dr Roper and Dr Gilchrest declared no relevant financial relationships. Dr Lim reports grants and research funding to his university from Allergan, Estee Lauder, and Ferndale Laboratories.

American Academy of Dermatology (AAD) Annual Meeting. Presented March 3, 2017.

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