Can Vitamin D Protect You From the Flu?

Vitamin D, termed the sunshine vitamin because it is produced by skin exposed to sunlight, has been in the news a lot recently. We are well familiar with the need for vitamin D to develop strong bones, but a rash of recent studies show that vitamin D also functions as an important regulator of immunity. Vitamin D deficiency is seen in many immune-mediated diseases such as Crohn’s disease, type 1 diabetes, multiple sclerosis, rheumatoid arthritis and asthma. Vitamin D deficient states have also been theorized to increase susceptibility to infections. Because vitamin D is mostly obtained from sunlight, blood concentrations of vitamin D decrease in the winter months, a time when influenza infections become more widespread.



A study released ahead of publication in the American Journal of Clinical Nutrition is one of the first clinical trials to report that vitamin D supplementation in school-aged children can decrease the incidence of influenza A. In this study, a randomized group of 334 children in Japan were given either 1200 IUs of vitamin D or a placebo over a four month period (December 2008 trough March 2008). The study showed a significant decrease in influenza A infection in the children who took vitamin D supplements. Vitamin D increases the production of antimicrobial proteins that inhibit some forms of the influenza virus, and vitamin D’s anti-inflammatory properties may also lessen flu symptoms.


Some of the study results were not as distinctly positive. A decrease in incidence of influenza B was not seen in this study. Various strains of flu have different mechanisms of infection within the body, and some may be more resistant to the effects of vitamin D. Children with asthma did not show a decrease in the occurrence of flu, but it is thought that asthma suffers are more prone to infection overall. Interestingly, the study showed that there were significantly less asthma attacks in the vitamin D supplemented group. Flu incidence was not decreased in the first month of supplementation; previous studies have shown that vitamin D supplements need to be taken for three months before blood concentrations reach a steady value. Therefore the optimal time to begin vitamin D supplementation would seem to be before the start of flu season. The skin loses its ability to make vitamin D from sunlight beginning in mid fall. Flu season typically peaks in November and April. Thus it has been recommended to supplement vitamin D from October through April.


Clearly, more research needs to be done to determine whether or not vitamin D supplementation can prevent the flu in larger, more diverse populations. We know that senior adults are more susceptible to influenza. Vitamin D requirements are also increased in this population as older skin is less efficient at making vitamin D. Overweight or obese individuals have also been shown to have low levels of vitamin D; one study showed that 1 in 3 women and 1 in 2 men were deficient in vitamin D. Though it has not yet been definitively determined that vitamin D supplementation prevents the flu, supplementation with up to 2000 IUs of vitamin D has been shown to be safe, and emerging evidence suggests that it may indeed help to prevent infection with some strains of the virus.

National Nutrition Month® 2010: Nutrition from the Ground Up

This March celebrates the thirtieth year of National Nutrition Month® whose purpose is to focus attention on healthy eating and physical activity habits to promote health and wellbeing in the American population. It’s difficult to compete in the current food environment with the message of health. You most likely won’t see any TV commercials or advertisements online or in print. But the message for this year resonates; “Nutrition from the Ground Up.”


I asked my family what this meant to them. This year’s theme brings to mind acres of plants growing in the sunshine with various shades of green and gold as far as the eye can see. My six year old daughter thought of butterflies. My mind met hers in a field of strawberry blossoms in May with butterflies fluttering in the air. The thought of foods grown using sustainable practices that are good for the environment and good for us comes to mind. Such practices encourage the butterflies and the bees to pollinate the plants, which then allow the fruits and vegetables to develop. The ground provides the nutrients for growth. So “Nutrition from the Ground Up” means caring for the earth that produces an abundant harvest to nourish us.

Another concept for this theme is the idea of gathering or foraging for food. Mushrooms, nuts, legumes, and wild berries are gathered in forests, groves and meadows and can often be found near the ground (nuts historically were collected on the ground after falling from trees). The nutrients these foods provide are varied with myriad health benefits. Although we are not gathering and foraging for these foods ourselves anymore, we should include them in our diets routinely to reap the health benefits that they provide. A variety of nuts provide heart-healthy fats to prevent heart disease and stroke; they range from omega-three polyunsaturated fats in walnuts to monounsaturated fats in cashews, almonds and peanuts. Legumes (peas, beans, lentils, and soybeans) are a wonderful combination of soluble and insoluble fiber with a good dose of protein; they help to manage blood sugar levels, which can help in the management of diabetes. Foraging for food also includes a level of physical activity. This physical activity used to be our way of life, but is now so greatly lacking on any given day. We should wander the ground again in our pursuit of health and vitality.

Perhaps the deepest issue here deals with something that is hidden under the ground. Like an iceberg, there is so much more to discover underneath. The iceberg analogy is one that I commonly use when describing the science of nutrition: what we currently understand about the interplay of nutrients on our health is only a small part of the story. Most of it is vast and hidden from view, despite all of our science. Dedication and patience is required to learn about the wonders yet undiscovered, just the same as the dedication and patience we must have in the pursuit of our health goals, whether they involve weight loss or disease management. “Nutrition from the Ground Up” speaks of discovery; finding a carrot buried deep within the ground, discovering how nutrients impact our health, and finding that healthier and happier person within ourselves.

Ask what “Nutrition from the Ground Up” means to you and your family.