Dec 27, 2010 11:35 GMT  ·  By

Sunlight helps life thrive not just by providing heat and light for plants' photosynthesis, but also by helping the immune system become stronger, and vitamin D produced by the body in response to sunlight is very important for humans' development.

A new research carried out by the Massachusetts General Hospital (MGH), concluded that newborns with low levels of vitamin D are at increased risk for respiratory infections.

During winter, it is quite difficult to achieve adequate levels of vitamin D, and in newborn babies, this seems to predict their risk of respiratory infections during infancy and the incidence of wheezing during early childhood, but not the risk of developing asthma.

So, the researchers wanted to see the exact relationship between the actual blood levels of vitamin D of newborns and the risk of respiratory infection, wheezing and asthma.

To do so, they analyzed data from the New Zealand Asthma and Allergy Cohort Study, following over 1,000 children in the cities of Wellington and Christchurch.

For the study, several measures were taken, including samples of umbilical cord blood from newborns enrolled by their mothers.

The moms also filled in questionnaires inquiring for respiratory and other infectious diseases, the frequency of wheezing, and any diagnosis of asthma – 3 and 15 months later and then, every year until the children reached the age of 5.

The researchers tested the cord blood samples (from 922 newborns in the study cohort) for levels of 25-hydroxyvitamin D (25OHD) – considered the most precise measurement of vitamin D levels.

Disturbingly enough, over 20% of them had 25OHD levels less than 25 nmol/L – considered very low, being twice as like to have developed respiratory infections as those with levels of 75 nmol/L or higher, by the age of 3 months.

The average level of 25OHD is 44 nmol/L, and some still consider it deficient, believing that the target level for most individuals should be as high as 100 nmol/L.

Children born in winter, those of lower socioeconomic status and with familial histories of asthma and smoking, had lower 25OHD levels, and the results of the survey concluded that over the first five years of life, the lower the neonatal 25OHD level, the higher the cumulative risk of wheezing during this period.

What was odd though, was that no significant association was found between 25OHD levels and a physician diagnosis of asthma at age 5.

Carlos Camargo, MD, DrPH, of the Massachusetts General Hospital (MGH), and leader of the study, said that “our data suggest that the association between vitamin D and wheezing, which can be a symptom of many respiratory diseases and not just asthma, is largely due to respiratory infections.

“Acute respiratory infections are a major health problem in children.

“For example, bronchiolitis – a viral illness that affects small airway passages in the lungs – is the leading cause of hospitalization in US infants.”

Most people only know that vitamin D is important for maintaining strong bones, but ignore its value for the immune system.

Camargo's previous studies show that children of women who took vitamin D supplements during pregnancy were less likely to develop wheezing during childhood.

But the kids enrolled in this study took very little supplements, their vitamin D levels being set mainly by exposure to sunlight.

Also an associate professor of Medicine at Harvard Medical School, Camargo stresses that the study results do not mean that vitamin D levels are unimportant for people with asthma.

He says that “there's a likely difference here between what causes asthma and what causes existing asthma to get worse.

“Since respiratory infections are the most common cause of asthma exacerbations, vitamin D supplements may help to prevent those events, particularly during the fall and winter when vitamin D levels decline and exacerbations are more common.

“That idea needs to be tested in a randomized clinical trial, which we hope to do next year.”

The results of this study are published in the January 2011 issue of Pediatrics.