Low vitamin D levels linked to colds
Individuals with low levels of vitamin D may be more likely to catch colds or flu, a new study suggests. Vitamin D is found in many foods, including milk, eggs, cheese and beef. Exposure to sunlight also helps the body produce vitamin D. Recommended daily intakes range from five to 15 micrograms, depending on a person's age and health.
Preliminary evidence suggests vitamin D may play a role in immune function. However, these earlier studies have not been conclusive. In this latest study, researchers analyzed data on vitamin D levels and respiratory infections in 18,883 individuals (aged 12 and older) who participated in the Third National Health and Nutrition Examination Survey (NHANES III) from October 1988 to October 1994.
Infections more Common
The researchers found that cold and flu infections were significantly more common among those with the lowest vitamin D levels (less than 10 nanograms per milliliter of blood) compared to those with the highest levels (30 or more nanograms per milliliter of blood). On average, they were 36 percent more likely to develop upper respiratory tract infections.
These results were consistent throughout the spring, summer and fall and were strongest among those with histories of asthma or chronic obstructive pulmonary disease (COPD).
However, additional research is needed to determine if vitamin D supplementation can help prevent infections. The authors call for randomized controlled trials in this area.
B-Vitamins may Help Prevent AMD
A recent study suggests that supplementation with B-vitamins may help prevent age-related macular degeneration (AMD), the leading cause of blindness in older Americans.
The study, funded by the National Institutes of Health and published in the Archives of Internal Medicine, included 5,205 women older than 40 years of age who did not have signs of AMD. The women were part of a large study looking at the effects of vitamins in women with heart disease or at least three risk factors for heart disease.
In April 1998, the participants were randomly assigned to receive supplementation (2.5 milligrams of vitamin B9 (folic acid), 50 milligrams of vitamin B6 and one milligram of vitamin B12) or placebo daily. Therapy continued through July 2005, and participants were monitored for the development of AMD through November 2005.
The authors found that women in the supplementation group had a 34 percent lower risk of developing AMD and a 41 percent reduced risk of developing AMD with significant vision loss compared to those in the placebo group. According to the authors, these protective effects were observed about two years after treatment started.
While the potential mechanism of action for these effects is unclear, these B-vitamins have been shown to lower blood levels of the amino acid homocysteine. Elevated levels of homocysteine are associated with an increased risk of developing coronary artery disease (CAD) and have been suspected of damaging blood vessels. However, it is unclear if reducing homocysteine levels would have beneficial effects on the heart.
