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Vitamin D and Longevity
Vitamin D is best known for building strong bones, but it may have another benefit: longevity. A Harvard analysis of more than 18 studies involving nearly 60,000 people, those who took vitamin D supplements had a 7 percent reduction in mortality from all causes compared with those who didn't take the vitamin. The numbers improved slightly for people who took vitamin D for three years or more. They had an 8 percent lower risk of dying.
Beyond the proven bone benefits, vitamin D is critical for immunity, prompting production of antimicrobial substances that seem to act like natural antibiotics and antiviral agents. Some experts think that the reduced sun exposure during winter could help account for the seasonal ebb and flow of colds and influenza. It previously was a mystery why influenza disappears in the summertime.
Emerging research also points to a role for vitamin D in cancer prevention, particularly against breast, colon, prostate and lung tumors. Vitamin D could help with cancer treatment. One recent study found that lung cancer patients who either got a lot of sun or had a high intake of vitamin D had three times the survival rate of their counterparts with lower vitamin D levels.
Another possible benefit of vitamin D is prevention of Type 2 diabetes, which affects an estimated 17 million Americans. Based on population studies, vitamin D deficiency during pregnancy may play a role in the worldwide increase of childhood autism.
So how could one vitamin have so many potentially wide-ranging effects? Unlike other vitamins, D acts both as a vitamin and as a hormone that can be activated as needed by the body.
This wider role of vitamin D has led scientists to weigh whether the current recommended daily intake is high enough. In the meantime, a growing number of experts advise routine measurement of vitamin D blood levels to detect deficiencies that aren't severe enough to produce clinical signs.
Vitamin D testing runs at least $100 per test. Also. no optimal blood levels have been set for the vitamin. (Unlike the international units used to gauge intake of vitamin D, blood levels are measured in nanograms per milliliter.) It is proposed that 30 to 40 nanograms per milliliter is a "reasonable target."
With age, the skin's ability to produce vitamin D drops significantly. Adults 65 or older make only 25 percent of the vitamin D produced by those ages 20 to 30.
Here are steps you can take to make sure you get enough vitamin D:
Eat salmon or mackerel. Just 3.5 ounces of either provides 90 percent of the daily value for vitamin D. Other foods naturally rich in vitamin D include sardines, tuna, eggs and liver. Foods fortified with vitamin D include milk, margarine and some breakfast cereals.
Just 20 minutes of sun exposure without sunscreen enables the skin to produce about 20,000 IU of vitamin D. You'd have to drink about 400 glasses of milk to get that same amount. And contrary to taking mega doses of dietary supplements, it appears that sun exposure does not cause toxic levels of vitamin D.
Take a vitamin D supplement. The National Academy of Sciences sets 200 IU per day as the adequate intake for those 19 to 50 years old; 400 IU for adults 51 to 70; and 600 IU for those 71 or older. In the latest study that showed the 7 percent reduction in mortality, the average intake was about 500 IU per day.
Many calcium supplements also contain vitamin D, providing between 200 and 400 IU. And single vitamin D supplements are another option. Signs of toxicity, which include bone loss and kidney problems, begin at about 10,000 IU daily.
87-8 A & D Vitamins 25000 / 1000 IU 120 gel caps $11.95 Ingredients: Vitamin A, Vitamin D. The vitamin content is entirely derived from natural fish liver oil with no chemicals or additives.
58-1 Calcium Citrate with Minerals 100 Tablets $14.95
85-3 Liquid Calcium and Magnesium 12 fl oz $16.00
Low vitamin D levels linked to poor physical performance
Older people with low levels of vitamin D may be at increased risk for poor physical performance and disability, according to a study released in April 2007.
With a growing older population, we need to identify better ways to reduce the risk of disability. The study showed a significant relationship between low vitamin D levels in older adults and poorer physical performance.
Calls for raising the recommended daily allowance of the vitamin have been growing after reports that higher intakes could protect against osteoporosis and certain cancers.
The study analyzed data from the InCHIANTI study, involving 976 people (average age 74.8) from two towns in the Chianti area of Italy.
Participants completed a short physical performance test of their walking speed, ability to stand from a chair and ability to maintain their balance in progressively more challenging positions. Additionally, their handgrip strength was also measured.
The researchers report that low levels of vitamin D were associated with five to 10 percent lower scores of physical performance and grip strength.
Vitamin D plays an important role in muscle function, so it is plausible that low levels of the vitamin could result in lower muscle strength and physical performance. It's also possible that those with poor physical performance had less exposure to sunlight resulting in low vitamin D levels.
Current recommendations call for people from age 50 to 69 to get 400 international units (IUs) of vitamin D per day and for those over age 70 to get 600 IUs. Many researchers, however, suggest that higher amounts may be needed.
Higher amounts of vitamin D may be needed for the preservation of muscle strength and physical function as well as other conditions such as cancer prevention. The current recommendations are based primarily on vitamin D's effects on bone health.
Calls to increase vitamin D intake have been growing. Indeed, only recently fifteen experts from universities, research institutes, and university hospitals around the world called for international agencies to "reassess as a matter of high priority" dietary recommendations for vitamin D because current advice is outdated and puts the public at risk of deficiency (The American Journal of Clinical Nutrition, Vol. 85, pp. 860-868).
A recent review of the science reported that the tolerable upper intake level for oral vitamin D3 should be increased five-fold, from the current tolerable upper intake level (UL) in Europe and the US of 2000 International Units (IU), equivalent to 50 micrograms per day, to 10,000 IU (250 micrograms per day).
Recent findings showing the importance of vitamin D status on multiple health outcomes underscore the need for more research on the effects of low vitamin D levels in elderly populations.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive. The latter is derived from plants and only enters the body via the diet.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
Source: Journal of Gerontology: Medical Sciences
April 2007
Authors: D. Houston, G. Schwartz, S. Kritchevsky, M. Cesari, L. Ferrucci, D. Maggio, A. Cherubini, M.A. Johnson, B. Bartali
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