Some
studies have suggested the vitamin from sunshine boosts the immune system and
helps prevents colds, some cancers and heart disease.
However
there is still a lack of clear scientific evidence to support many of these
claims.
Researchers
from the University of Otago, Christchurch, are engaged in a large scale study
of vitamin D (called the Vitamin D and Acute Respiratory Infection Study or
VIDARIS) and have published a new paper on its effect on the common cold.
The
study, published in the latest edition of the prestigiousJournal of
the American Medical Association(JAMA), found that taking vitamin D
supplements did not result in participants having fewer or less severe episodes
of upper respiratory tract infections.
Adult
participants (more than 300 Cantabrians) took either a placebo pill or a
vitamin D pill every month for a year and half.
Researchers
measured the number and severity of participants’ colds during this time.
They
found no statistical difference between those taking the placebo pills and
those given vitamin D supplements.
VIDARIS
principal investigator Professor David Murdoch says there has been considerable
speculation about the potential role of vitamin D in preventing a variety of
infections, including the common cold.
“Up
to now we have lacked evidence to support any benefit from well-designed
studies, despite so much money being spent on supplements.”
“VIDARIS
is the first study to convincingly show that vitamin D does not prevent colds
in healthy adults. However, it is important to note that very few people in our
study had extremely low levels of vitamin D at the beginning. So, our findings
may not apply to these people and to children who should now be the focus of
further research.’’
Vitamin
D supplements may still be of benefit for bone health and for the prevention of
other conditions, Professor Murdoch says.
The VIDARIS study is also looking at whether vitamin D prevents other
infections, including carriage in the nose of staphylococcal bacteria.
September
marks the start of spring but new research reveals it is also the month when
Australians' vitamin D levels are at their lowest ebb.
The
University of Sydney study also shows vitamin D deficiency affects more
Australians and lasts longer than previously believed.
"Our
results suggest that the current guidelines for both vitamin D testing and the
use of supplements need to be reviewed," said Professor Steven Boyages
from Sydney Medical School.
Professor
Boyages and his PhD student Kellie Bilinski recently published their findings
in Clinical
Endocrinology.
"This
is the largest ongoing Australian study on vitamin D deficiency ever
undertaken," said Professor Boyages.
"Vitamin
D deficiency is implicated in a number of serious diseases including diabetes
and cancer so improving our understanding is critical.
"The
fact that the government-subsidised cost of testing for deficiency was $96.7
million in 2010 and rising is another reason better knowledge is
important."
The
study looked at vitamin D levels (by studying the presence of a metabolite) in
over 24,000 samples taken from walk-in patients and inpatients in NSW between
July 2008 and July 2010. It investigated the effect of age, gender, season,
socioeconomic status and remoteness on results.
"Our
study indicates that large segments of the Australian population are at risk of
deficiency for prolonged periods of the year, particularly during autumn to the
end of spring. The prevalence of deficiency was higher and more persistent than
previously reported, ranging from 33 percent in summer to 58 percent in spring.
The seriousness of the deficiency was also greater than in most other
Australian reports."
The
study found that vitamin D levels peaked in summer, reaching a maximum in
January for women and February for men, before declining gradually in late
summer and falling sharply in the winter months. They reached their lowest
point not in winter, as previously reported, but in early spring.
"Even
by December, the first month of summer, levels were still 46 percent below
their peak. Although levels of ultraviolet-B radiation, the body's principal
source of vitamin D, would be rising by then, this reflects the time it takes
to replenish the body's stores."
Current
testing guidelines do not address the need to taken seasonal variation into
account.
"Ideally
testing would occur in spring when vitamin D levels reach their lowest
concentration. If an individual is found to be deficient a subsequent test
three months afterwards would see if they have been able to replenish their
vitamin D," said Professor Boyages.
"Similarly
use of vitamin D supplements currently fail to address this factor of seasonal
variation. A modified approach would see the use of supplements commence, or
increase, at the end of summer and be maintained until the end of spring when they
would either be stopped or reduced depending on an individual's sunlight
exposure."
The
study also found that a previously unidentified at risk group is females
between 20 and 39 years of age. Further investigation is required to determine
the underlying cause for the higher prevalence of vitamin D deficiency in this
and other groups.
Steven Boyages is affiliated with Westmead Hospital and eHealth NSW
Initiative and Kellie Bilinski with Westmead Breast Cancer Institute.
