MINERALIZATION IN CASE OF OSTEOPOROSIS: VITAMIN D
Vitamin D is vital for the absorption of calcium into your body for proper bone mineralization. The D.H.S.S. has no recommendation for adult intake of vitamin D, but children, adolescents, pregnant/ lactating women and the housebound need 10 micrograms daily.
You get most of your vitamin D from the sun, with the ultraviolet (UV) light in sunshine converting a substance in your skin to a pre-vitamin D. This pre-vitamin is then changed in the liver and kidneys to its active form, the hormone calcitriol, necessary to maintain constant blood calcium levels for the normal functioning of nerves and muscles. Your body is not actually synthesizing vitamin D while you are in the sunshine, as it takes three or four days for your system to complete the process and ‘recharge your batteries’. How much sunshine are you getting every day?
Invisible UV light cannot penetrate ordinary window glass, so in order to soak up those rays you have to be outdoors. The Earth’s surface is protected by the upper layers of the atmosphere with ozone molecules in the stratosphere absorbing most of the near ultraviolet. Pollution at ground level may increase the ozone layer still further and interfere with the overall strength of the radiated light, so it is difficult to measure how much UV you are getting.
According to a research team at Harvard Medical School, you need about fifteen minutes to one hour of sun exposure each day, to fill your vitamin D needs, if you are a lightly pigmented person. Transmission of light depends on the thickness of your skin’s outer layers. After you reach the age of forty or fifty, there is a steady decline in the ability of your skin to produce that pre-vitamin D, as your skin thins with age (coupled perhaps with a lesser performance from your liver). So the skin of a woman in her seventies makes about half the vitamin D produced by her twenty-year-old granddaughter under the same conditions.
There are many variables: How intense is the sun? Is it winter or summer? Do you live in a northern latitude or the ‘Sun Belt’? The incidence of hip fracture is highest in the north of Scotland and lowest in the south of England, in studies related to the hours of sunshine and its effect on body stores of vitamin D.
Are you at a high altitude? At high altitudes and near the equator, the UV level is greater than at sea level or in northern latitudes. How clear is the air? Do you have smog and pollution? The low angle of a winter sun blocks much of that UV light, as the rays have to pass through more of our planet’s ozone layer, and smog, smoke and fog can block out still more UV.
Do you have a light or a dark skin? If your skin is naturally dark with the pigment melanin, it can screen off as much as 95 per cent of the UV light from the skin layers making pre-vitamin D. It is estimated that a black person needs five times as much exposure to the sun as a fair-skinned person to produce the same amount of vitamin D. When darker pigmented people move from the south to the lower intensity of a northern sun, they can become vitamin D-deficient. For instance, Arab and Indian women, accustomed to living in seclusion or heavily veiled, have been found deficient in the vitamin when going to live under the cloudy skies of Britain. So let the sun get to your bones!
As the sun is at its strongest and most harmful between 10 a. m. and 2 p.m., sunning in the early morning or late afternoon is less damaging to your skin than the middle of the day.
, If you use one of the sunblockers or sunscreens, wait about fifteen minutes when out in the sun before applying. These preparations may prevent the sun-related production of vitamin D in your skin.
Beware of excessive sunbathing which is both unnecessary and unhealthy. Most people think it fashionable and fun to be tanned. Millions of fair-skinned people now live in the ‘Sun Belt’ though their skin may be sun-sensitive and burn rapidly.
Sunlamps and sunbeds using UV light have been popular for providing a tan in winter and more recently tanning salons have been established in some cities. Dermatologists agree that concentrated doses of UV can cause skin damage, so the potential for short- or long-term injury is there, whether the UV radiation is from sun or lamp, with the result being premature wrinkles and, more seriously, a risk of malignant melanoma. This once-rare cancer has been doubling about every twelve years since World War II with a death rate in women faster than from any other malignancy other than lung cancer. Queensland, Australia, had an influx of fair-skinned people after World War II, and seven to ten years later they saw a large increase in melanoma there. If you notice any changes in colour or size of moles or scar tissue, see your doctor immediately.
The elderly need to take special precautions against overexposure to the sun and high temperatures, particularly if you are obese or have diabetes or heart disease. Certain types of drugs can create a vitamin D deficiency, but others when combined with excessive sunshine, can bring on photosensitive or phototoxic effects. Drugs that can create problems when taken along with heavy doses of sunshine are: some tranquillizers, anti-hypertensives, diuretics, tetracycline antibiotics, sulpha drugs, oral diabetic drugs and quinidine. If you are taking any prescription or non-prescription medicines, check first with your doctor or pharmacist for possible reactions in strong sunlight.
And make sure your eyes are protected during sunning -research suggests that prolonged exposure to UV over many years can contribute to the premature development of cataracts and tumours.
Getting a healthy exposure to sunshine every day is the best way for your body to acquire vitamin D, but there are dietary sources if you can’t get outdoors or if skies are smoggy.
Because medical authorities were concerned several years ago about possible deficiencies in vitamin D, with few natural sources in food, it was decided to fortify certain items. Margarines and lowfat spreads are required by law to be fortified with 2.25 micrograms of vitamin D per ounce. Some dairies and food firms also fortify skimmed or semi-skimmed milk, evaporated milks, yogurts, dried milk powders and breakfast cereals.
Other foods with naturally present vitamin D are some saltwater fish (herrings, salmon and sardines, for instance), cod-liver oil and halibut-liver oil, egg yolks, liver and cheese.
Vitamin D is stable in cooking and not lost by heating or processing, but it is affected by rancidity in oils. Hence if oils, butter and margarine become rancid, the active vitamin is destroyed.
For better absorption, it’s more desirable to get this vitamin from sunshine, but you may need supplementary amounts of vitamin D, especially in winter, if you are:
breast-feeding, or
elderly, living in a town or housebound,
a shift-worker (nurse, for example) working mainly at night,
heavily wrapped in clothes, and
rarely eat dairy products.
use heavy make-up.
The NACNE report (from the National Advisory Committee on Nutrition Education) also recommends that Asian schoolchildren be given vitamin D supplements.
By springtime you may have depleted your store of vitamin D. Records indicate that bones fracture most frequently in winter and early spring, when daylight is short, sunshine scarce and when vitamin D and calcium reserves are low. Multi-vitamin preparations usually contain vitamin D, and calcium supplements are often augmented by the vitamin.
However, you can have too much of a good thing: because vitamin D is fat-soluble and stored in the liver, large quantities from over-supplementation can be toxic, cause kidney damage, or trigger the creation of kidney stones. The toxic dose varies among individuals, but toxicity has occured at levels as low as 50 to 125 micrograms daily. When large amounts of vitamin D supplements (over 25 micrograms) are taken without sufficient calcium, bone depletion may occur. (In contrast, your skin has a built-in system that shuts down synthesis of vitamin D after a certain amount of UV exposure, eliminating the danger of toxic effects from sunning.)
Discuss your needs with your doctor before embarking on any tablet supplementation.
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Posted in Healthy bones Osteoporosis RheumaticTags: Healthy bones
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