Don’t take D for granted


BY the time we reach adulthood, most of us have a general knowledge of what’s good and bad for our health… hopefully. Eating fresh fruits and vegetables – good. Drinking a litre of whiskey or cola – bad. Exercising a few of times a week – good. Playing in the sun without sunscreen – bad.

Well, Dr Michael F. Holick, a professor of medicine, physiology and biophysics at Boston University Medical Center in the US agrees with the first three ideas, but disagrees with the last – that going in the sun without sunscreen is bad for you.

With more than 30 years of experience in his profession and having authored more than 300 research papers in peer-reviewed medical journals, including the New England Journal of Medicine, the Lancet, and Science, Dr Holick is a tireless crusader for sensible sun exposure.

Beyond strong bonesContrary to common wisdom, vitamin D isn’t just about strong bones. Researchers used to think that vitamin D receptors were found only in certain places such as bone, intestines and kidneys. However, we now know that vitamin D receptors are everywhere in the body, including our body’s immune system.

Recent studies have shown there is evidence that vitamin D is also responsible for strengthening the immune system and lowering disease risk. Cancer patients have been found to have low levels of vitamin D in their blood compared to their healthy counterparts. Hence, low levels of vitamin D have been associated with elevated cancer risk. These cancers include breast, prostate and colorectal cancer.

The Johns Hopkins Colon Cancer Centre has mentioned that the new prescription for colon cancer prevention may soon include an afternoon in the sun, followed by a tall glass of milk.

Several new studies in the past year have shown that by maintaining adequate serum vitamin D levels, individuals may successfully prevent colon cancer, as well as several other cancers.

Vitamin D is a fat-soluble vitamin that is found in some foods, and can also be made by your body upon exposure to ultraviolet (UV) light from the sun.

Researchers in the US National Cancer Institute also reported on the protective effect of vitamin D in preventing colorectal cancer mortality. After following the vitamin D status of 16,818 participants for 12 years, they determined that vitamin D exhibited a strong protective effect against colorectal cancer.In further support of vitamin D, a recently completed epidemiological study of over 190,000 individuals showed that both calcium and vitamin D (from food and supplements) were protective against colorectal cancer. However, the researchers reported mixed results for men and women: “Total vitamin D intake was inversely associated with colorectal cancer risk in men but not in women.”

How do we obtain vitamin D?

The body makes vitamin D upon exposure to UV rays from sunlight. The amount of vitamin D made when the skin is exposed to sunlight depends on multiple factors such as age and skin colour, to how much of the skin is exposed, as well as length of exposure, geographical location and time of the day.

Even cloud cover and haze affects vitamin D production. Sunscreen also blocks some UV rays, which reduces the body’s ability to produce vitamin D.

According to the US-based Vitamin D Council, a non-profit organisation responsible for disseminating accurate information on vitamin D, it is estimated that a third to half of the adult population worldwide are vitamin D3 deficient. Take note that living in tropical sunny Malaysia does not mean we are getting enough of this sunshine nutrient.

Other sources of vitamin D3 include food and supplements. Some good sources of vitamin D are fatty fish such as salmon, mackerel, tuna and sardines, as well as cod liver oil. Another good source of vitamin D is fortified milk. Beef liver, cheese and egg yolks contain lesser amounts.

Vitamin D3 (cholecalciferol) is the type of vitamin D the body naturally produces in the skin in response to sun exposure. Vitamin D2 is produced naturally when fungi (yeast or mushrooms) are exposed to UV light from the sun or artificial UV light.

There is evidence that the body has preference to D3 over D2, with studies showing that the body more readily uses D3 when it has both forms in the body, and that D3 is more potent than D2 for producing 25-hydroxyvitamin D, which is then converted to the active form of vitamin D.

The Institute of Medicine was able to set a recommended daily allowance (RDA) for vitamin D in 2010. The RDA of vitamin D for children and adults up through age 70 is 15 micrograms (equal to 600 International Units, IU) per day. The RDA is 20 micrograms (800 IU) a day for adults older than 70. The safe upper limit for adults was set at 100 micrograms (4,000 IU) per day.

When taking a vitamin D supplement, try to choose a supplement made with natural vitamin D3 (cholecalciferol).