Vitamin D levels linked to respiratory disease

Having severe vitamin D deficiency may put people aged 65 years and older at more than twice the risk of having self-reported respiratory disease, according to an article published online May 6 in theJournal of the American Geriatrics Society.

However, the question remains as to whether respiratory disease is a cause rather than a consequence of low vitamin D concentrations.

Vasant Hirani, PhD, from the Department of Epidemiology and Public Health, University College London Medical School, United Kingdom, analyzed the records of 2070 people (1120 women) who participated in the 2005 Health Survey for England and who were also interviewed by a nurse and had a blood sample taken.

Dr. Hirani found that after adjusting for age, sex, season, smoking status, and social class, people with less than 35 nmol/L serum 25(OH)D were more than twice as likely to report having respiratory disease as those individuals with a serum level of 64 nmol/L or higher. Individuals with intermediate serum levels also had greater risk compared with those with levels above 64 nmol/L.

Prevalence of respiratory disease among the study population ranged from 8.9% for people with vitamin D levels of 75 nmol/L and greater to 45.5% for people with levels of 25.0 to 49.9 nmol/L. The association was not consistent, however, as only 14.7% of individuals with serum 25(OH)D levels lower than 25 nmol/L reported having respiratory disease.

Although Dr. Hirani found associations in unadjusted analyses between low vitamin D levels and smoking tobacco, lower social class, fair or poor general health, and self-reported heart disease, cancer, and pain, she found no associations between low vitamin D levels and age, sex, body mass index, alcohol consumption, or use of vitamin supplements.

It is "biologically plausible" for vitamin D to be associated with respiratory health, she writes, because of vitamin D's role in the lung's immunity response to virus infection.

"It is also likely that individuals with a respiratory condition are less likely to spend time outdoors and may also limit their activities, resulting in less sunlight exposure and thus vitamin D deficiency," she writes. More research is needed to clarify the cause and effect of the association, she notes.

Although definitive conclusions as to whether low vitamin D is truly linked to respiratory disease, she writes, the study population is nationally representative of people of that age in England.

She concludes, "Regardless of the direction of causation, the higher-than-expected co-occurrence of vitamin D deficiency and respiratory conditions is an important public health question for older populations living in northern latitudes because both are common, and both have substantial adverse health consequences."

Dr. Hirani is currently funded by the National Health Services Information Centre and is an editor and chapter author on the Health Survey for England, funded by the English Department of Health.