Our skin evolved to create vitamin D when exposed to ultraviolet rays of the sun (UV) rays. So, when the majority of the world's population lives in or near the equatorial regions, people had no shortage of nutrients, with their bodies making 10000 to 20000 international units (IUs) of this vitamin each day.

GOT MILK? Mandatory fortification of this drink explains why most children meet the recommended intake of vitamin D through their diet - and why so many adults milk not shy.

However, over the millennium, more and more people moved to high latitudes, where up to half of the year, exposure to solar UV radiation is not enough to feed the production of vitamin D in the skin. More recently, justifiable concerns about sun and skin cancer have prompted increasing shares of people, even at high latitudes-Don sun-blocking clothing. Unfortunately, what is good for skin protection is bad for the production of vitamin D naturally.

It can also be harmful to health, a series of studies has recently indicated. For decades, vitamin D can be seen in large part for his role in increasing the absorption of calcium, which is important for bone health. However, during the last decade, and especially the past 5 years, research has linked a wide range of additional benefits to having enough vitamin D. 'S shown that the fight against cancer nutrient and diabetes, is the key raw material for a hormone that protects the muscles and inhibits autoimmune disorders from multiple sclerosis and lupus to inflammatory bowel disease (SN: 10 / 9 / 04, p. 232).

Moreover, many of these newly recognized the benefits of vitamin D rely on blood concentrations of nutrients far beyond those needed to protect the bone. Although high by the standards of the diet is not really mega doses, explains Bruce W. Hollis of the Medical University of South Carolina. Rather, they reflect amounts typical of what people can generate, naturally, within your skin, if he spends much time outdoors in a low latitude.

However, with modern habits and routines of work, few of us create these high doses of vitamin D in our bodies throughout the year. Therefore, we are confident in our diet most of this essential nutrient, though few foods are naturally rich sources of vitamin D and only a few, such as milk, are supplemented by something more than meager amounts (see case that fortified foods Be Even More?).

Although vitamin pills can provide much or all of the USA Recommended daily intake (RDI) of D for children and adults-200 and 600 IU, depending on the age and bone mineral researchers have lately been recommending that people are much, much more (SN: 10/16/04, p. 248). In fact, some scientists have advised the federal government to boost RDI of vitamin D until at least 1000 IU and to bump the insurance certificate beyond the current limit of 2000 IU.

Within this context, several research teams have been exploring whether residents of the USA Meet the current RDA. The answer, based on some data presented earlier this month at the Experimental Biology (EB), held in San Diego, is disappointing: Many of us are well below even the current, conservative RDIs.

Seniors: Do not lead by example

Michael F. Holick of Boston University School of Medicine and his colleagues analyzed the diets of about 16500 people chosen as a representative sample of the entire population of the United States. The researchers used data that have been collected as part of a federation National Health and Nutrition Survey between 1999 and 2000.

The meeting of EB, which reported that children 1 to 8 years old were most likely to get the RDI of vitamin D. Approximately 60 percent is obtained from the diet alone-largely because milk is fortified with vitamin D, and this is an age group that downs lots of milk. If one of the accounts of additional inputs from vitamin supplements, roughly 80 percent of children shall conform with the current R & D + I unless they are black. Fewer than 50 percent of young people in the RDI to meet vitamin D through diet, and even vitamin pills bump up the total to only 65 percent.

People from 9 to 50 years managed, as a rule, to get almost as much vitamin D as young children, although a far higher proportion of their vitamin D supplements came from. Especially in young women, only 20 to 40 percent typically has the RDI of vitamin D from diet alone.

Vitamin D deficiency reaches epidemic proportions among people over 50. Only about 5 percent of these men and 1 to 3 percent of women of their R & D to get the nutrient from the diet alone. Supplement use bumps up the share of elderly R & D to get about 35 percent of whites, 17 percent of Hispanics and about 10 percent black.

These values are particularly worrisome because people of color have a harder time making vitamin D naturally. The reason? His dark skin pigment filters much of the ultraviolet light from the sun.

Heavy observation

Because rural Americans tend to spend more time outdoors than their urban counterparts do, which traditionally have had greater exposure to the sun and vitamin D concentrations in the blood.

However, Hollis and his coworkers found that today, even rural populations do not always get the vitamin D they may need. The researchers suggest that the spread of obesity may be a contributing factor.

The team analyzed blood concentrations of vitamin D for about 30 rural adults and 13 urban areas. In winter, the mean concentration of the vitamin in the blood is low for both groups, says team member Brittany Gorres State of South Dakota. His team reached mean values of vitamin D of 14 nanograms per milliliter (ng / ml) in the city and people from 20 ng / ml in the rural group. She adds that hormone data from these recruits indicated that blood values below about 27 to 30 ng / ml might compromise bone health.

Summer blood concentrations of vitamin D were higher for both groups: 27 ng / ml in rural individuals and 39 ng / ml in the urban dwellers. However, Gorres notes, many individuals within each population remained low, with some never having more than 10 ng / ml in the blood, summer or winter. Moreover, he adds, a trend emerged: Lean people tend to fall into the higher end of the range of vitamin in each group, overweight people at the bottom.

"It has been proven, time and again, that obesity is a risk factor for vitamin D deficiency," says Hollis. "The mechanism? That, in fact nobody understands," he adds. "Once vitamin D is dedicated to fat, which does not come out well," he observes, so "[body] fat appears to act like a sponge."

But the problem can be remedied with a supplement of vitamin D, he adds. Hollis gives the example of a student who worked in his laboratory last fall. Because of its highly pigmented skin and obesity, which may be concerned about vitamin D deficient, and recommended that have tested the blood of the vitamin. She did, and the analysis showed that her blood had only about 7 ng / ml, which is "gravely deficient," says Hollis. However, after the student took 4000 IU of vitamin D per day for 3 months, Hollis said, "they finally got their blood levels in the mid-30's."

Although 4000 IU per day-10 times a young woman of the RDI-might sound high, Hollis acknowledges, "we have found that nursing mothers need about 6000 IU per day to transfer enough vitamin D in milk provide adequate amounts to an infant. " He is currently managing 2000 IU per day for women throughout their pregnancies as part of a 5-year National Institutes of Health-funded study. The participants in each of these trials live in South Carolina, he noted, so they should have access to a lot of vitamin generation of UV rays throughout the year.

The picture emerging, Hollis said, is that people are not getting even the current RDI of vitamin D for a variety of reasons-where they live, how long they typically spend outdoors, their skin pigmentation , and, perhaps, their weight. However, it seems that many people still need higher amounts than the RDI to build muscle strength and prevent disease.