Two new studies on vitamin D have thrown up important information with one showing that levels of vitamin D have dramatically decreased among Americans over the last two decades and the second that older people can prevent fractures by taking supplements as long as they use a high dose and are consistent.

Lead researcher Dr. Adit Ginde, an assistant professor of surgery at the University of Colorado, Denver School of Medicine said, "We found a marked increase in vitamin D deficiency over the past two decades. Over three out of every four Americans now have vitamin D levels below what we believe is necessary for optimal health. African-Americans and Hispanics are at particularly high risk -- nearly all have suboptimal levels."

In the first study published in the March 23 issue of the Archives of Internal Medicine, Ginde's group collected data from the Third National Health and Nutrition Examination Survey, on vitamin D levels in 18,883 people between 1988 and 1994, and 13,369 people between 2001 and 2004.

The researchers found that from 1988 to 1994 the average vitamin D levels were 30 nanograms per milliliter and this went down to 24 nanograms per milliliter from 2001 to 2004. They also found that over the study period vitamin D levels of less than 10 nanograms per milliliter increased from 2 % to 6 % and there were fewer people with vitamin D levels of 30 nanograms per milliliter or higher, a shift of 45 % vs. 23%).

Blacks had the greatest reduction of vitamin D levels and levels of vitamin D of less than 10 nanograms per milliliter rose from 9 % to 29%, and levels of more than 30 nanograms per milliliter or higher dropped from 12 % to 3%.

"Increases in vitamin D deficiency in the population may have reduced the overall health of the population," Ginde said. "Since sunlight is the body's major source of vitamin D, increases in sunscreen, sun avoidance, and overall decreased outdoor activity, while successful in reducing skin cancers, has probably reduced vitamin D levels in the population."

"Vitamin D is an important and underappreciated public health issue and may be responsible for some racial differences in health outcomes," Ginde said. "Most Americans could use more vitamin D. Higher doses of vitamin D supplementation than currently recommended, at least 1,000 to 2,000 IU daily, are likely needed to raise vitamin D levels for many people."

The second study reported in the same journal which highlights the importance of vitamin D for bone health was conducted by Swiss researchers who reviewed the findings of 12 randomized clinical trials which looked at the benefits of vitamin D supplements in reducing fractures in adults aged 65 and older. In all, the trials involved 42,279 participants, and looked at non-vertebral fractures; with eight of the studies specifically focusing on hip fractures.

The researchers found, supplements cut the risk of any non-vertebral fracture by 14% and of hip fractures by 9%. While quantities below 400 IU a day had no effect on fracture risk, people who consumed more than 400 IU daily had a 20 % lower risk of any type of fracture and an 18 % lower risk of hip fracture.

Lead researcher Dr. Heike A. Bischoff-Ferrari of the University of Zurich said, "Everyone age 65 and older should take vitamin D in a dose close to 800 IU per day, best as vitamin D3, and with good adherence."

She added that the younger adults could follow this as well. "I think if you are young and want to do something early for your bone health that's something to think about."

The researchers said low levels of vitamin D have been associated with rickets in children and lower bone mineral density in adults and recent research has also linked insufficient vitamin D to cancer, heart disease, infection and poorer health overall. Optimal levels range from 30 nanograms per milliliter to 40 nanograms per milliliter.

Bischoff-Ferrari and her team noted that adherence to the supplement was needed to reap the benefits. "A lot of people think a healthy nutrition is good enough, but unfortunately vitamin D is very hard to cover by food sources," Bischoff-Ferrari added.