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progressively increasing doses of vitamin D3 which started at 28,000 IU and progressed to 280,000 IU. Mean serum 25-hydroxyvitamin D levels rose from 78 to 386 nmol/L. Adverse effects were sought by monitoring serum calcium levels, the urinary ratio of

calcium to creatinine,

creatinine, electrolytes

,

liver enzymes, serum protein,

serum and

parathyroid hormone. None were found. In particular, these huge doses of vitamin D caused neither elevated serum or urine calcium levels. The authors conclude that the data support the feasibility of pharmacologic doses of vitamin D for clinical research and as well provide objective evidence that vitamin D intake beyond the current upper limit of 2000 IU/day is safe by a large margin. They also point out that there is already evidence that daily doses of 4000 and 10,000 IU/day are safe. This so- called Phase I study concerned with the issue of safety and was not powered to detect changes in

The authors point out that their study is consistent with the strong protective effect of sun exposure during childhood (6-15 years) found in a case- control study conducted in Tasmania. The protective effect (risk reduction) of averaging 2 or more hours per week of sun exposure compared to less than 2 hours was 69%. In addition, they mention a study where indoor and outdoor workers exhibited a dose-dependent protective effect of sun

exposure

on

MS-related

mortality.

The

present

study

is

especially

important

because

it

eliminates

questions about inheritable factors influence these and other studies.

that

might

have

The mechanism involved in the protective effect is unknown, but MS is an autoimmune disease and exposure to sunlight could, according to the

authors, produce immunosuppressive

protection mechanisms

.

by several Or sunlight

clinical outcomes in the patients involved. Kimball, S.M. et al. Safety of Vitamin D3 in Adults with Multiple Sclerosis. American Journal of Clinical Nutrition, 2007, Vol. 86, pp. 645-51.

CHILDHOOD SUN EXPOSURE AND MULTIPLE SCLEROSIS: A STUDY OF TWINS This study from the University of California in Los Angeles examines the influence of childhood sun exposure on the risk of multiple sclerosis (MS) in monozygotic twins, i.e. twins originating from a single egg that have the same gender and identical genetic constitution. By doing this, the investigators eliminated confounding by genetic susceptibility. They recruited a total of 79 twin pairs with MS where there was a quantifiable difference in sun exposure between the pair and where only one twin had MS. A sun exposure index dependent on nine sun exposure related activities was developed to provide a numerical evaluation of sun exposure for each individual. It was found that each of the nine sun exposure related activities during childhood seemed to convey a strong protection against MS in this group of twin pairs, that is, the MS free twin had significantly higher sun exposure index or score than the MS member of the pair. Sun tanning, for example, reduced the risk by 60% for the twin who spent more time at this activity compared to the co- twin. Finally, when the data was stratified by gender, the benefit of sun exposure was restricted to only the female sets of twins. The authors of this beautifully designed and executed study conclude that sun avoidance seems to precede the diagnosis of MS and that this protective effect is independent of genetic susceptibility.

produced vitamin D could suppress the production of cytokines associated with MS activity. The authors also suggest that the fact that the protective effect was only seen in female twin pairs suggests that there may be a sex-specific vitamin D mediated immunomodulation as has been seen in animal studies. Islam, T, et al. Childhood Sun Exposure Influences Risk of Multiple Sclerosis in Monozygotic Twins. Neurology,

2007, Vol. 69, pp. 381-88.

VITAMIN D AND CARDIOVASCULAR RISK A national survey designed to estimate prevalence of common chronic conditions

the and

associated risk factors was conducted between 1988 and 1994 (NHANES III).

in the US It provided

a

database

which

is

constantly

mined

for

information about specific questions.

A study based

on this data was recently published which addresses the question of the association between vitamin D status and the prevalence of risk factors for cardiovascular disease (CVD) using the vitamin D serum marker 25-hydroxyvitamin D. Data for over

15,000

adult

participants

were

available.

When

individuals with 25-hydroxyvitamin D levels than 52 nmol/L were compared with those levels equal to or greater than 92 nmol/L, it found that those in the low-level group

less with was had

significantly hypertension,

higher abnormal

probabilities of have blood glucose, history of

diabetes,

obesity,

and

high

triglycerides.

However,

for

two

prominent

risk

factors,

high

total

cholesterol

or non-HDL cholesterol, no The authors claim that

correlations were found. to the best of their

knowledge this is the first study significant association between low

to demonstrate vitamin D status

and

CVD

risk

factors

in

a

nationally

representative

International Health News

November 2007

Page 6

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