Do May gray and June gloom depress vitamin D levels? Quite possibly

Ultraviolet B (UVB) rays help produce vitamin D in the skin.
sun behind clouds

What was it that Little Orphan Annie sang in “Tomorrow”?

The sun'll come out
Bet your bottom dollar
That tomorrow
There'll be sun!

Indeed, the summer ahead promises to be sunny and hotter than average, according to the National Oceanic and Atmospheric Administration. In the meantime, however, health-conscious residents of Southern California might be forgiven for wondering whether the weeks of unrelenting “May gray” and “June gloom” have messed with their vitamin D levels.

The answer, according to John S. Adams, MD, is quite possibly, especially in those who have an underlying bone disease such as osteoporosis.

A Distinguished Research Professor in the Department of Orthopaedic Surgery at the David Geffen School of Medicine at UCLA, Dr. Adams plays key roles in the Clinical and Translational Science Institute, funded by the National Institutes of Health, and UCLA’s Alpha Stem Cell Clinic, which is supported by the California Institute for Regenerative Medicine. He also heads UCLA’s Vitamin D Research Lab.

Dr. Adams, 74, is convinced that vitamin D does not get enough respect.

“The government doesn’t even recommend that individuals my age with osteoporosis be screened for vitamin D deficiency, even though vitamin D deficiency is one of the causes of accelerated bone loss,” he said.

Vitamin D is a nutrient that the human body needs to build and maintain healthy bones. Unless vitamin D is present, the body cannot absorb calcium, the primary component of bone.

Vitamin D also serves as an anti-inflammatory and an antioxidant that can counteract the effects of unstable molecules, known as free radicals, that damage DNA and cell membranes.

The ‘sunshine vitamin’

In the early 20th century, vitamin D seized the spotlight when researchers realized that cod liver oil (which contains vitamin D) and sunlight could cure rickets, a bone-softening disease, then rampant among poor children who suffered from bowlegs.

In 2011, Dr. Adams and other researchers found that vitamin D plays an essential role in the body’s ability to battle infections such as tuberculosis, a potentially fatal lung disease.

Although vitamin D is known as the “sunshine vitamin,” it is, in fact, a hormone, just like cortisol or thyroid hormone.

Vitamins are synthesized in various plants and are conveyed to animal bodies chiefly through food. In other words, they aid growth and metabolism through what is called a “direct nutritive effect.”

Hormones are chemical substances that are produced in one part of the body and travel through blood to other parts of the body.

Vitamin D is produced in the skin from a form of cholesterol called 7-dehydrocholesterol. Sunlight, which is a mixture of different wavelengths of light, is the key to that production. The wavelengths that make vitamin D are in the ultraviolet B (UVB) range and are relatively high energy. They can penetrate the skin of human beings and other animals. (Most mammals, birds and reptiles produce vitamin D in their fur, feathers or skin.)

The energy converts the precursor — 7-dehydrocholesterol — into vitamin D3.  

For people attempting to get adequate vitamin D from sunlight, the recent conditions along the California coast have posed a challenge. Water droplets, like those in the region’s pervasive coastal clouds and fog during this year’s gloomy spring, refract or reflect the UVB photons, or light particles.

“It’s like a natural sunscreen,” Dr. Adams said. “You won’t really sunburn, and you won’t really make vitamin D under those conditions.”

Dr. Adams said his own experience provides a textbook case. He grew up in Kansas playing baseball, football and basketball outdoors and getting all of the vitamin D he needed during summer months. Once he began spending most of his time indoors as a grownup, he had to get vitamin D by other means.

How to get the right amount

Like patients who spend most of their time inside, patients with darker skin can suffer from vitamin D deficiency, Dr. Adams says. Melanin, or skin pigment, tends to absorb the UV wavelengths that kickstart vitamin D production.

Supplements can help, he says, especially given that overexposure to sunlight and its UVB rays can cause sunburns, as well as melanoma and other skin cancers, in patients with dark and light skin. Vitamin D is also found in some dairy products (including all milk in the United States, which is fortified with vitamin D), fish, oysters and fortified cereals.

Patients with low bone mass disorders such as osteoporosis should ask their doctors to monitor their vitamin D levels to ensure that they are getting the right amount from supplements. Too much vitamin D can cause a high blood-calcium level. Too much calcium in the blood can cause a patient to pass too much calcium in urine, possibly leading to kidney stones.

In a recent trial approved by the U.S. Food and Drug Administration, Dr. Adams and a colleague at a company that produces vitamin D supplements found that supplements improved outcomes for unvaccinated people who contracted COVID-19. Higher levels of vitamin D in the blood led to significantly faster resolution of coughing, chest congestion and shortness of breath.

“It’s highly likely,” Dr. Adams said, “that we don’t fully understand all of the functions of vitamin D.”

Martha Groves is the author of this article.

Take the Next Step

Learn more about the Vitamin D Research Lab at UCLA.