News

Aug 25, 2023

Low vitamin D linked to increased risk of developing long COVID

Around 1 in 5 adults in the U.S. who get COVID-19 eventually develop long COVID,

Around 1 in 5 adults in the U.S. who get COVID-19 eventually develop long COVID, according to the Centers for Disease Control and Prevention (CDC).

But long COVID affects 50% to 70% of people who’ve been hospitalized with COVID-19, according to a new study that explores a link between vitamin D deficiency and long COVID.

The researchers looked at vitamin D levels of people with COVID-19 upon hospital admission and again six months after discharge. They observed that those with long COVID had lower levels of vitamin D than those who did not have the condition.

Lead investigator Dr. Andrea Giustina, professor of endocrinology and metabolism at the University Vita-Salute San Raffaele, in Milan, Italy, told Medical News Today:

"The clinical area of long COVID in which we found a more relevant influence of low vitamin D was the neurocognitive one."

The findings of the research were recently published in The Journal of Clinical Endocrinology & Metabolism.

The World Health Organization (WHO) defines long COVID as a continuation or appearance of COVID-19-related symptoms within three months of an acute SARS-CoV-2 infection. The symptoms, which may last for two months or longer, have no other explanation.

The National Institutes on Aging (NIH) describes the following symptoms of long COVID:

For the study, researchers recruited 50 people diagnosed with long COVID and 50 people who did not develop the condition from an outpatient clinic associated with San Raffaele Hospital in Milan.

Individuals in the two groups were matched one to one, taking into account the severity of their illness from COVID-19, as well as age, sex, and any preexisting chronic conditions.

The close matching of people with and without long COVID was a means to avoid as many influencing factors as possible that might confuse the study's findings. Uncontrolled variables in studies of vitamin D, and of long COVID, are difficult to account for.

At the six-month follow-up, the authors of the study found no other observable differences between their matched participants than their vitamin D levels, suggesting vitamin D deficiency as a driver of long COVID symptoms.

The researchers also found that greater vitamin D deficiencies were most often associated with the neurocognitive symptoms synonymous with long COVID.

While vitamin D obviously plays a role in keeping bones healthy, Dr. Giustina explained that "extra-skeletal effects of vitamin D are well-known. Among those, the positive effects on the immune system can be thought to play a role in this connection."

Ray Marks, PhD, a lecturer of health and behavioral studies at Columbia University, told MNT that "it would be hard to refute" the study's findings since other research is consistent with them.

Dr. Marks noted that studies indicate that vitamin D affects cognitive health, pain, obesity, and bone health, all of which, she said, "parallel long COVID and multiple chronic diseases."

Similarly, she added that older adults having lower vitamin D levels is a common finding and that this can lead to other potentially long COVID symptoms such as cognitive disturbances, frailty, and weakness.

"The molecular mechanisms of vitamin D alone imply it is a necessary cell physiology and gene mediator with enormous organism implications if insufficient. Hence, results appear to be what one might expect, but this would need to be carefully studied."

– Ray Marks, PhD

Dr. Marks also noted that other studies have established that people with dark skin are more likely to have vitamin D insufficiency.

For instance, the Cooper Institute reports that vitamin D deficiency affects as many as 76% of African Americans. The melanin in darker skin tones is believed to reduce the production of vitamin D.

Vitamin D is indirectly produced by sunlight. Ultraviolet B rays cause the skin to synthesize a form of cholesterol, 7-dehydrocholesterol, which the body uses to make vitamin D3 in the liver and then the kidney.

The National Institutes of Health (NIH) states that most Americans have adequate blood levels of vitamin D, although 1 in 4 do not.

Dr. Marks cited air pollution as being among the widespread factors that may be responsible for a decrease in vitamin D levels.

The only way to know if you’re getting enough vitamin D is to have your doctor prescribe a vitamin D blood test.

The NIH recommends that adults ages 19 to 70 receive an average of 600 IU of vitamin D daily. Older adults should receive a daily average of 800 IU.

If your blood test results indicate a vitamin D deficiency, your doctor will recommend the dosage of vitamin D supplementation that suits your needs.

When asked if vitamin D supplementation could help prevent long COVID symptoms, Dr. Giustina said: "The role of vitamin D supplementation in the prevention of long COVID [is] not yet available."

Even so, Dr. Giustina recommends checking patients’ vitamin D levels as a precaution post-hospitalization and treating any deficiency as necessary.

"I am in favor of daily safe levels of vitamin D for all, for both prevention and recovery of multiple chronic health conditions including obesity, a key COVID analog," Dr. Marks said.