A recent study led by Queen Mary University of London provides the most evidence yet that vitamin D has benefits beyond bone and muscle health, and could have major implications for public health policy, including the fortification of foods with vitamin D to tackle high levels of deficiency. The study was conducted by a consortium of 25 investigators from 21 institutions worldwide and funded by the National Institute for Health Research.
The results, published inTheBMJ, are based on a new analysis of raw data from around 11,000 participants in 25 clinical trials conducted in 14 countries including the United Kingdom, the United States, Japan, India, Afghanistan, Belgium, Italy, Australia and Canada. Individually, these trials yielded conflicting results, with some reporting that vitamin D protected against respiratory infections, and others showing no effect.
Respiratory Infection Protection
Lead researcher Professor Adrian Martineau from QMUL said: "This major collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections. Our analysis of pooled raw data from each of the 10,933 trial participants allowed us to address the thorny question of why vitamin D worked in some trials, but not in others.
"The bottom line is that the protective effects of vitamin D supplementation are strongest in those who have the lowest vitamin D levels, and when supplementation is given daily or weekly rather than in more widely spaced doses, she said. Vitamin D fortification of foods provides a steady, low-level intake of vitamin D that has virtually eliminated profound vitamin D deficiency in several countries. By demonstrating this new benefit of vitamin D, our study strengthens the case for introducing food fortification to improve vitamin D levels in countries such as the UK where profound vitamin D deficiency is common."
The Sunshine Vitamin
Vitamin D - the sunshine vitamin - is thought to protect against respiratory infections by boosting levels of antimicrobial peptides - natural antibiotic-like substances - in the lungs. Results of the study fit with the observation that colds and flu are commonest in winter and spring, when levels of vitamin D are at their lowest. They may also explain why vitamin D protects against asthma attacks, which are commonly triggered by respiratory viruses.
Daily or weekly supplementation halved the risk of acute respiratory infection in people with the lowest baseline vitamin D levels, below 25 nanomoles per liter. However, people with higher baseline vitamin D levels also benefited, although the effect was more modest - 10 per cent risk reduction. Overall, the reduction in risk of acute respiratory infection induced by vitamin D was on a par with the protective effect of injectable flu vaccine against flu-like illnesses.
Acute respiratory infections are a major cause of global morbidity and mortality. Upper respiratory infections such as colds and 'flu are the commonest reason for GP consultations and days off work. Acute lower respiratory infections such as pneumonia are less common, but caused an estimated 2.65 million deaths worldwide in 2013. Vitamin D supplementation is safe and inexpensive, so reductions in acute respiratory infections brought about by vitamin D supplementation could be highly cost-effective.
The Link Between Exercise And Vitamin D
Johns Hopkins researchers recently reported that an analysis of survey responses and health records of more than 10,000 American adults for nearly 20 years suggests a synergistic link between exercise and good vitamin D levels in reducing the risk of heart attacks and strokes.
Both exercise and adequate vitamin D have long been implicated in reducing heart disease risks, but in a new study the researchers investigated the relationship between these two health factors and their joint role in heart health. Their findings, which were published in theThe Journal of Clinical Endocrinology & Metabolism, identified a positive and direct relationship between exercise and vitamin D levels in the blood, which may provide evidence that exercise may boost vitamin D stores.
They also found that the two factors working together seemed to somehow do more than either factor alone to protect the cardiovascular system. The researchers caution that their study is an observational one and that long-term, carefully controlled clinical trials would be needed to establish evidence for cause and effect. Nevertheless, the study does support the notion that exposure to the sunshine vitamin D and exercise are indicators of good health.
In our study, both failure to meet the recommended physical activity levels and having vitamin D deficiency were very common saysErin Michos, M.D., M.H.S.,associate director of preventive cardiology and associate professor of medicine at the Ciccarone Center for the Prevention of Heart Disease at the Johns Hopkins University School of Medicine. The bottom line is we need to encourage people to move more in the name of heart health.
Healthy Diet And Lower Body Fat
Michos adds that exposure to a few minutes a day of sunlight in non-winter seasons, eating a well-balanced meal that includes oily fish such as salmon, along with fortified foods like cereal and milk, may be enough to provide adequate levels of vitamin D for most adults. But Michos says that sun exposure may not be the whole story of the direct relationship found between exercise and vitamin D levels, since vitamin D produced by the skin after exposure to sunlight tends to level off when the body makes enough, and the levels in the studys participants didnt show signs of doing so.
She says this points to evidence that there may be something else going on in the body that causes vitamin D and exercise to positively influence levels of each other. For example, people who exercise may also have other healthy habits that influence vitamin D levels such as lower body fat and a healthier diet. Alternatively, people who exercise may take more vitamin supplements.
As for the racial disparity they saw, this could mean promoting physical activity may not be as effective for raising vitamin D levels in African-Americans as in whites. Michos notes that people with darker skin produce vitamin D less efficiently after sun exposure, possibly due to the greater amount of melanin pigment, which acts as a natural sunscreen. African-Americans also tend to have lower levels of 25-hydroxyvitamin D overall but they dont seem to experience the same consequences, such as bone fractures, that whites have with similarly low levels.
Michos cautions that people who meet the recommended daily amount of 600 to 800 International Units a day and who have adequate levels of vitamin D dont need to take additional vitamin supplements. More isnt necessarily better once your blood levels are above 20 nanograms per milliliter, says Michos.
Sunlight And Sunscreen
People at risk of bone diseases, have seasonal depression, or are obese should have their physicians measure vitamin D levels to ensure theyre adequate, but for many, the best way to ensure adequate blood levels of the vitamin is from sun exposure, healthy diet, being active and maintaining a normal body weight, she continued. Just 15 minutes of sunlight in the summer produces about 3000 international units of vitamin D depending on latitude and skin pigmentation, which is equivalent to 30 glasses of milk. Just be sure to use sunscreen if you plan to be outside longer than 15 minutes.
While the health boost from regular physical activity is undisputed, the benefits of vitamin D supplements havent yet been proven for heart health. Michos notes that a recent randomized clinical trial published inJAMA Cardiologyfailed to show any cardiovascular benefit with high-doses of monthly vitamin D supplements among participants living in New Zealand. She says that larger studies including more diverse populations of patients and different dosing regimens are currently on-going and, when published, will provide further insight and guide recommendations for patients.