People with high levels of
vitamin D are better able to control their asthma. Vitamin D, also called the
sunshine vitamin, is formed in the skin mainly when exposed to sunlight. It can
also be obtained from the diet as well as through supplementation.
Vitamin D is converted to 25-Hydroxyvitamin D (25(OH)D)
in the liver. Earlier studies have shown that vitamin D supplementation in
children with asthma improves asthma control and suggested that increasing
25(OH)D levels could hold promise for future asthma health interventions.
The question now is, does outdoor
exposure, that is, exposure to sunlight influence the vitamin D levels in
children with asthma, and if so, then how much exposure is required?
To find out, Sonali Bose and her
colleagues at the Johns Hopkins University, Baltimore, studied 121 asthmatic
children aged 2 to 6 years. The children were from the part in Baltimore with
predominantly African-American people. The high prevalence of asthma in the
region is suspected to be due to air pollutants and unique allergens, lower
socio-economic status, and poor diet.
Serum 25(OH)D levels over a
6-month period were studied. Blood samples were evenly split across the seasons
- summer, fall, winter, spring. Serum IgE levels, which are indicative of
allergy, were also measured.
The findings were-
54 percent of the children were
found to be insufficient or deficient, with levels below the accepted
sufficient level of 30 ng/mL, and 23 percent of them were in the deficient
range with serum levels of 20 ng/mL or below.
About 7.4 percent of children
had 25-OH D levels less than 15 ng/mL, which is associated with the risk of
Vitamin D levels for the small
number of whites tended to be higher despite equivalent socio-economic status.
On an average, children, both
girls and boys, spent 3 hours outdoors daily. No association was found between the hours spent outdoors and 25(OH)D
Interestingly though, children
who spent more than 5 hours per day
outside were not 25-OH D deficient
There was no observed
difference in 25(OH)D levels among the seasons, though according to the
National Institutes of Health (NIH) data, low vitamin D levels are more common
in African-American children, especially in the winter.
There was an inverse
correlation between 25-OH D levels and total IgE concentrations (immunoglobin
that plays an important role in manifestation of asthma and other allergic
'The implications of these
findings may be even greater in younger cohorts, as it is during early
childhood when considerable lung growth is still occurring, and when the
respiratory system may be particularly sensitive to nutritional and
environmental signals that induce changes in lung function,' report the
'Although UV light is necessary
for dermal vitamin D production, black urban children with asthma appear to be
unresponsive to what little daily sunlight they do receive, as higher daily
levels of outdoor exposure were not linked to higher 25(OH)D' the researchers
inferred, 'so, cutaneous synthesis alone during limited out door exposure is
not sufficient to raise serum levels effectively in black urban children'.
'A combination of limitations in sunlight exposure and
darker pigmentation may amplify the risk of vitamin D deficiency among black
urban children, contributing to greater asthma morbidity than their white counterparts,'
they concluded, and suggested further trials to determine whether increasing
serum levels can reduce asthma maybe with dietary supplementation.