Study Questions Benefits of Vitamin D Supplements

A new study challenges vitamin D's effectiveness to prevent colds or the flu. What does this mean for you?

Study Questions Benefits of Vitamin D Supplements

Vitamin D is a vital vitamin/hormone that can come from sunlight, diet, and some supplements. It bestows many health benefits including an improved ability to prevent some types of cancer.

However, a new study in the Journal of the American Medical Association questions vitamin D’s ability to prevent colds, the flu and other similar upper respiratory tract infections (URTIs), which include symptoms like runny nose, cough, sore throat, or nasal stuffiness.


Researchers followed 294 New Zealanders for 18 months. One-half of the participants received oral vitamin D3 supplements at specialized monthly dosages. The control group received a similar-looking placebo pill. All participants had normal vitamin D levels at the start of the study.

At the end of the observation period, the researchers noted a similar number of URTIs in both groups and concluded that monthly administration of vitamin D3 “did not reduce the incidence or severity of URTIs in healthy, predominantly European adults with near-normal vitamin D levels.”

Despite the results of this most recent study, don’t throw away your vitamin D supplements just yet. This study is one of several that has shown conflicting evidence of vitamin D’s cold-fighting effects. Another study on Mongolian schoolchildren in winter found that taking vitamin D supplements led to a 50% reduction in acute respiratory infections. It’s quite possible that the URTI-fighting effects of vitamin D supplements can vary between different populations or at different geographic locations, where sunlight exposure varies.

Furthermore, keep in mind that past epidemiological studies have shown an association between low vitamin D levels and various respiratory illnesses, including an increased risk of getting tuberculosis. Other researchers have touted vitamin D’s bug-fighting properties. It has been shown to reduce the body’s risk of infection by altering its “modulation of anti-microbial peptides (AMP)” and by “enhancing [the] clearance of invading organisms” in the respiratory tract, preventing infections.

These results may also suggest that taking vitamin D supplements, though helpful, may not entirely replace making a strong effort to increase levels of vitamin D in the diet or through sun exposure. The best dietary sources of vitamin D include salmon, tuna and mackerel (especially the flesh) and fish liver oils. Beef liver, cheese and egg yolks also contain small amounts.

Also, remember that vitamin D also plays a number of other beneficial roles in our bodies, including:

  • Promoting absorption of calcium and bone health
  • Boosting immune function
  • Reducing inflammation
  • Healthy neuromuscular function
  • Protecting against some forms of cancer

Our Daily Dose on vitamin D provides more information regarding its effects and vitamin D-rich foods.

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