Vitamins are essential nutrients that the human body cannot make. Since vitamin D is made in the body, it is not a true vitamin. Ultraviolet light B rays create it by changing a substance in our skin, which becomes vitamin D. (For the sake of simplicity, the term vitamin D has been used for the many chemical structures of D in the body.) The liver makes a minor change before vitamin D begins to circulate in the blood. It is then available to every cell in the body that needs it. Cells change it one more time, into an active material (with a very long name 1,25 dihydroxycholecalciferol) that they need.
Vitamin D type molecules seem to have been developed by microbes, perhaps billions of years ago, to protect themselves from damage by ultraviolet light. Plants and animals continue to make it when they are exposed to adequate sunshine. However, the molecule does much more than protect against sunlight. It changes the action of most of the cells in the body. In fact, it is a type of hormone! We now know that vitamin D regulates more than 50 genes in tissues throughout the body.
The list of effects is long and growing longer as more research is done on vitamin D. It is essential in infancy and childhood for strong bone growth and normal cell maturation. Lack of adequate vitamin D in infancy will lead to rickets. It must be absorbed during childhood and adolescence to build adequate bone mass for the rest of life. In addition, there is growing evidence that inadequate D levels in childhood put us at risk of developing certain diseases. Multiple sclerosis (MS), type 1 diabetes, rheumatoid arthritis and possibly inflammatory bowel disease could be the result.
Vitamin D influences cell maturation, stopping cells from increasing in number too quickly. This effect helps prevent cancer, particularly those of the colon, rectum, breast, ovary and prostate. Many other cancers are also being studied. It has been estimated that 50,000 to 70,000 lives in the U.S. and 30,000 to 35,000 lives in the U.K. are lost each year due to premature death from vitamin D-preventable cancers.
A lack of vitamin D increases muscle and bone pain, particularly in the elderly. Supplements improve muscle strength, lessen pain, and reduce falls in the elderly. Vitamin D affects the body’s reaction to some infections, and benefits the immune (defence) system. It also improves insulin release. This may eventually help those with type 2 diabetes. Vitamin D affects brain cell growth and ability to repair itself, and protects against effects of aging. It improves heart muscle function, particularly if the heart is in failure, and can lower blood pressure under some circumstances
Modified vitamin D molecules are being extensively studied for use against cancer and diabetes, and for disease prevention. They are already widely used against psoriasis (a skin condition). We expect to see far more use over the next few years.
There has been much debate over the past decade about how much vitamin D we need. The risk of too much must be balanced against giving too little.
The last official guidelines, from 1997, are far out of date. They recommended 400 International Units (IU) of vitamin D per day for infants, then 200 IU per day for everyone until age 50. The amount increases to 400 IU per day until age 70, and then 600 IU per day after that. Most multivitamin preparations contain 200 or 400 IU.
Too much vitamin D may cause high calcium levels in the blood. However, recent studies show that ‘too much’ may be 10,000 IU per day or more.
The major source of vitamin D for humans has always been sunshine. Those who live in the tropics and spend time outside often have blood levels in the 100 to 200 nmol/L level. The best possible amount is considered to be 80 to 200 nmol/L. However, average levels in Canada are between 40 and 60 nmol/L. Thirty-five per cent of children three to 16 years have levels below 40 and almost none are above 80 nmol/L. A study in Calgary showed 35 per cent of adults had levels below 40 nmol/L.
In the south of Canada, we can only make vitamin D in our skin from about April to September. In the north, this is possible for even less of the year. Cloud and smog decrease D production in the skin. From October to March the sun is too low in the sky, even if it is Alberta bright.
Rickets was a major public health problem in Canada until the 1950s. At that time, the government required that vitamin D be added to all fluid milk. To this day, in Canada, only fluid milk has significant D added (see box). However, many do not drink milk because of culture, taste, or allergy. Is that a problem? Yes. A study at Stollery Children’s Hospital in Edmonton, done in April 2003 on healthy children showed that 98 per cent had mild to severely inadequate blood levels of vitamin D.
Much research over the past decade has examined both oral intake as well as blood levels of vitamin D. It is clear that the official recommendations do not allow for the best possible blood levels in Canadians. Infants and children should take a supplement of least 400 IU a day, in addition to what they get from formula and food. (Breastfed babies in particular must be supplemented with 400 IU of vitamin D a day.) In general, this will provide an average 600 IU per day. The upper acceptable limit of vitamin D from all sources for infants in their first year of life is 1000 IU per day. Teens and adults require at least 2000 IU of Vitamin D from all sources per day.
Between 11 am and 3 pm during the summer months, the sun is high enough in the sky to make D in the skin. As an easy rule of thumb, if your shadow is shorter than your height, your skin can produce D! Ten minutes of sunshine on the skin two to three times per week is enough for pale skin. More time is necessary for those with darker skin. Sunscreen can then be applied.
Studies of tanning salon users have shown that this is a legitimate source of vitamin D. However, dermatologists (skin doctors) express concern about excessive exposure to sunshine or tanning lights.
Some people rarely expose their skin to the sunshine, including teens that sit at computers all day, children in school, elderly in care facilities, and those of certain cultures and fashion habits. For these people, vitamin D must be taken by mouth all year long.
Roughly 40 IU per kilogram of body weight each day will provide adequate but not excessive D intake. If in doubt, ask your doctor to check your D level after you have taken a supplement for a month. Those with chronic liver or kidney disease should talk to their doctor before taking a supplement.