New vitamin D guidelines expected to boost targets

The Institute of Medicine is reviewing its 1997 guidelines for vitamin D intake, and will likely recommend increased supplementation when new guidelines are published in 2010.

There is a growing consensus that currently recommended intakes — 200 IU per day for individuals under age 50 and 400 IU for those aged 50-70 — are too low, the director of the department of food and nutrition at Purdue University, West Lafayette, Ind., said.

In addition to vitamin D’s well-known effects on bone metabolism, levels in the range of 1,000 IU per day have been associated with good outcomes in recent controlled and epidemiologic trials that examined risks for falls in the elderly and for type 2 diabetes.

Also, 1,000 IU is well below the 2,000 IU upper limit of vitamin D cited in the existing guidelines, as said at Scripps Health: Natural Supplements: An Evidence-based Update.

The IOM is not likely to recommend that people spend a lot more time in the sun as a way of increasing vitamin D, advice that would run counter to skin cancer prevention efforts. Further, “you cannot eat enough vitamin D-containing foods to get anywhere near 1,000 IU of vitamin D per day.”

“Research has shown that levels much higher than 2,000 per day showed no evidence of harm. So the upper limits will likely change along with the new intake recommendations.”

Osteoporosis prevention is the strongest rationale for increasing vitamin D intake. Daily supplementation with 700 IU vitamin D and 500 mg calcium reduced the 3-year rate of first nonvertebral fractures by 5.5 percent, compared with placebo, in a cohort of 176 men and women aged over 65.

A National Health and Nutrition Examination Survey III data analysis showing improved bone mineral density in adults aged 50 years and older as serum vitamin D increased from 20 nmol/L to values over 80 nmol/L.

The same researchers published a meta-analysis of six large population studies showing that the relative risk of all bone fractures starts to decline when daily vitamin D intake increases to roughly 450 IU per day.

Although vitamin D plays a role in bone metabolism, its fracture-reducing impact may also have something to do with its effects on neuromuscular function and overall health status. Observational data from the NHANES III database showed that those with the highest vitamin D serum levels had the shortest times on the sit-to-stand test in large cohort of people aged 60-90 years.

Further, a study of 122 Swiss women in a geriatric hospital showed a 49 percent reduction in incidence of falls among the women taking 800 IU vitamin D plus 1,200 mg calcium for 3 months, compared with those taking calcium alone.

Low vitamin D level also is associated with increased risk of cardiovascular disease and, possibly, type-2 diabetes.

A Framingham Offspring study found a hazard ratio of 1.62 for cardiovascular events during a 7-year period for subjects with vitamin D levels less than 15 nmol/L. This was largely attributable to the 40 percent of subjects who were hypertensive.

According to the emerging story is vitamin D’s role in glucose metabolism and its potential for slowing insulin resistance and lowering risk for type-2 diabetes.

A new Framingham Offspring study involving 808 nondiabetic individuals showed a strong inverse correlation between serum vitamin D levels and fasting plasma glucose and fasting insulin, as well as homeostatic model assessment (HOMA) for insulin resistance. Vitamin D showed a positive correlation with insulin sensitivity, plasma adiponectin, and HDL cholesterol.

In an analysis of data on nearly 84,000 women in the Nurses Health Study, researchers at Tufts University found a 13 percent reduced relative risk of type 2 diabetes in the women taking the higher vs. lowest amounts of supplemental vitamin D.

The Tufts researchers also studied 314 white, nondiabetic people randomized to supplementation with 500 mg calcium plus 700 IU vitamin D or placebo for 3 years. Among those with impaired fasting glucose at baseline, the supplements attenuated the rise in fasting glucose at the 3-year point vs. placebo.

Overall, the findings suggest that vitamin D and calcium supplementation at moderate doses can slow the progression of hyperglycemia and insulin resistance.