Vitamin D: The truth behind the headlines

Helen Cowan

Benefits beyond bones?

Vitamin D (consumed in the diet or made in the skin in response to sunlight) is essential for strong bones; deficiency can result in rickets in children and osteomalacia in adults. Beyond bones, headlines suggest that vitamin D could be a miracle cure. Is it just hype or is there room for hope?

Vitamin D & multiple sclerosis

Reasons for hope

After diagnosis with MS, vitamin D is sometimes taken: reduced relapses and slowed symptoms have been reported. That MS is more common in countries with less sunlight, where vitamin D levels are lower, has further raised hopes that vitamin D could be useful in the management of MS. (MS is also more common in babies born in the spring, when late stages of pregnancy will have coincided with darker months and less vitamin D production).

Vitamin D might act to promote nerve cell development or to protect nerve cells from attack (MS is considered an autoimmune disease in which the immune system attacks nerves); vitamin D may even regulate genes affecting MS risk.

Results from trials

In one trial, 25 people with MS took high dose vitamin D; some clinical improvement, and no side effects, were seen and bigger trials are underway.

Vitamin D and cancer

Reasons for hope

“Living at higher altitudes with lower exposure to sunlight (and so less vitamin D) is linked to increased cancer risk”. “Studies have associated increased vitamin D intake with decreased risk of cancer” says the Cochrane Library, drawing on research data.

Vitamin D is actually a hormone—and can bind to cells and affect their ability to divide. When it comes to cancer (when cells grow and divide in an uncontrolled manner), it’s possible that vitamin D might curtail cell division, and even kill cancer cells.

Results from trials

“The available evidence on vitamin D and cancer occurrence is intriguing but inconclusive” says the Cochrane Library. After studying 18 trials, involving more than 50,000 patients, vitamin D did not affect rates of cancer.

Occasionally a study will show lower rates of cancer in people with higher levels of vitamin D. Beware the hype in the headlines though: it could be that low vitamin D levels are a consequence of having cancer (since you are more likely to stay indoors and be sun-deprived)—rather than a cause. The vitamin D/cancer question remains a vital one—and the VITAL study, at Harvard Medical School is currently testing just that, among more than 25,000 people.

Vitamin D and asthma

Reasons for hope

During an asthma attack your airways become inflamed and it’s harder to breathe; a common trigger is a respiratory infection such as a cold or the flu. Vitamin D could defend through its anti-inflammatory, antiviral and antibacterial powers in the lungs.

Results from trials

In trials involving adults and children with mild to moderate asthma, vitamin D reduced the average number of asthma attacks. Whether vitamin D helps all asthmatics—or just those who are D-deficient—is still in doubt. 1 billion people worldwide are deficient in vitamin D: a daily dose might just help some to breathe easier.

Vitamin D and the heart

Reasons for hope

Scientists have often observed that those with lower vitamin D levels have a higher risk of heart attack—but are not yet sure whether there’s a direct link between vitamin D levels and heart health since other factors that control heart attack risk (such as your weight, your diet and how much time you spend outdoors) can also affect your vitamin D level.

Results from trials

The evidence just isn’t there yet—and, in fact, the results are conflicting. One study showed that vitamin D might help the heart to beat more strongly; another showed no effect on blood pressure or heartbeat.

However, doctors are worried that enthusiasm for vitamin D is outpacing the evidence when it comes to the heart. People are self-prescribing the vitamin, without yet knowing the effects of excess, making it harder to find people for clinical trials who have not already altered their vitamin D levels.

The Verdict on Vitamin D

Vitamin D could be a miracle nutrient—but we don’t yet have the definitive answer. Hope is deferred but definitely not dashed. As scientists delve deeper into the D-vitamin, they’re even debating whether it might have a role in infection, pain and autism. Watch this space.