Ellen Campbell-Grizzle
Scientists now know that the biologic effects of vitamin D are extensive. Many cite results from various studies showing the presence of receptors for vitamin D in a wide variety of cells to support claims that this hormone has diverse biologic effects and potential for greater health benefits.
Vitamin D is fat-soluble substance that acts like a hormone, regulating the formation of bone and the absorption of calcium and phosphorus from the intestine. It helps to control the movement of calcium between bone and blood. Many Jamaicans are aware of the link between the deficiency of vitamin D and the deformed bones seen in rickets. In adults, a lack of the vitamin causes a softening of the bones known as osteomalacia.
Most people, including infants, require little or no extra vitamin D from food if they are regularly exposed to sunlight. Bright sunlight is not necessary; even the sunshine on a cloudy summer day will stimulate formation of some vitamin D in the skin. Vitamin D cycles through the kidney and liver and is transformed into a potent steroid in the same chemical class as oestrogen.
Low or high levels
The term vitamin D usually refers to vitamin D3 also known as cholecalciferol, that is generated in the skin of animals and the plant form and vitamin D2 or ergocalciferol. There are dietary sources of vitamin D, including egg yolk, fish oil, herring, mackerel and a number of plants. Deficiencies may occur due to:
Genetic defects in the vitamin D receptor: a number of different mutations have been identified in humans that lead to hereditary vitamin D resistance.
Severe liver or kidney disease: this can interfere with generation of the biologically-active form of vitamin D.
Inadequate exposure to sunlight.
Low levels of vitamin D have been found in females in sunny countries where women have to be heavily veiled in public and private. Excessive exposure to sunlight does not lead to overproduction of vitamin D.
Vitamin D toxicity is usually a consequence of overdosing on supplements. Ingestion of milligram quantities of vitamin D over periods of weeks or months can be severely toxic to humans and animals. In fact, baits laced with vitamin D are used, very effectively, as rodenticides. An excess of the vitamin can cause loss of appetite, weight loss, nausea, headache, depression and deposits of calcium in the kidneys.
Vegans and vitamin D
Vegans usually obtain vitamin D from the action of sunlight on the skin or by taking fortified foods such as soya milk, margarine, breakfast cereals and vitamin supplements which are made from yeast or other fungi. Fortified vegan products usually contain D2.
Current research
Research is showing that receptors on many cells listen and respond to vitamin D. They have identified this hormone as one of the most potent inhibitors of the growth of normal and cancer cells. There is also the claim that it builds the immune system. One research team added vitamin D to a blood mix and noted that 'disease-fighting cells roared to life'.
Use with circumspection
Since we live on the sunny side of the world, pharmacists have always recommended vitamin D use with caution. However, new research is generating excitement about the use of the substance as part of therapy in various illnesses. The wise consumer should discuss this vitamin with their doctor or pharmacist before adding it to any medication mix
Ellen Campbell-Grizzle, president, Caribbean Association of Pharmacists; director, Information and Research, National Council on Drug Abuse; email: yourhealth@gleanerjm.com.
