Vitamin-D: The Sunshine Vitamin Comes Back Into the Light
Here in the U.S., experts have been warning the public about the cancer-causing effects of sunlight for at least the last 20 years. Sunshine causes skin cancer and melanoma, they have said, and it's important to cover up or use plenty of sunscreen.
Even in Australia, experts told the public to slap on the sunscreen and not to be shy about it. The result was that the incident of skin cancer in Australia decreased but an increased number of Australians and New Zealanders ended up with a vitamin-D deficiency. And now scientists say that vitamin-D deficiency may lead to skin cancer.
For years, nutritionists have known that sunshine wasn't the demon it was made out to be. Researchers back in the laboratory tested the effects of vitamin-D on the immune system and discovered that vitamin-D actually boosts the immune system instead of destroying it. The sunshine vitamin activates white blood cells to engulf bacteria, has anti-tumor activity and modulates the immune system. Vitamin D also activates natural killer cells, B cells and T cells. Vitamin-D also regulates the expression of cancer genes.
What Does Sunshine Have to Do with Vitamin D?
Vitamin D is a fat-soluble vitamin that can be either ingested or synthesized in the skin by exposure to sunlight. The sunlight activates a form of cholesterol present in the skin and converts it to vitamin D.
Vitamin D is found in both plant and animal tissue. There are at least five different forms, called D1, D2, D3, D4 and D5. Synthetic Vitamin D2 is called ergocalciferol. It is derived from fungal and plant sources. Natural vitamin D, vitamin D3, is called cholecalciferol and is derived from animal sources and also made in the skin. The term Vitamin D refers to all the different forms of these two substances. The natural form occurs in fish liver oils.
Vitamin D is Important for All Organs
One of the main functions of Vitamin D is to help absorb calcium and phosphorus from the intestinal tract. Without Vitamin D, children won't grow in height and their bones and teeth do not calcify as they should.
Another function of the sunshine vitamin is the maintenance of the organs. Vitamin D is essential for normal heart action, blood clotting, and a stable nervous system. Researchers have also discovered that Vitamin D affects the acidity of the gastric juice produced in the stomach, preventing ulcers.
Food Sources of Vitamin D
Fish liver oil and fatty fish are the only naturally rich sources of vitamin D. Fish liver oil is also high in vitamin A. The combination is great for nutritional status simply because vitamin A increases the amount of vitamin D that is absorbed by the body.
Three ounces of catfish, salmon, herring and mackerel provides between 300 and 425 IU. Three ounces of tuna provides 200 IU.
Milk, breakfast cereals, supplements, soy milk and protein bars are high in vitamin D only because they are fortified. One egg only provides 20 IU.
Ten to 20 minutes of sun exposure per day on exposed skin is enough to meet the recommended daily allowance. The U.S. Dietary Reference Intake Committee has determined that 200 IU is plenty for those up to the age of 50. After the age of 50, 400 IU is recommended up to 70 years of age, and the amount rises to 600 IU for those older than 70. However, during the winter months, 1000 IU is required daily for children and greater amounts for adults.
These levels have decreased over the years. Initially the recommended daily allowance was that 400 IU was needed per day for healthy individuals, including both adults and infants. Those with osteoporosis have been recommended to take up to 2000 IU per day.
In Canada, experts from the Canadian Cancer Society recommend that non-white adults take 1000 IU daily while whites take 1000 IU in the fall and winter. The Canadian Pediatric Society doubles that requirement to 2000 IU for pregnant and breastfeeding women.
Deficiency of Vitamin D
In a growing child, the lack of vitamin D creates a situation where the bones cannot withstand the stress of weight. The leg bones begin to bow outwards. The skull bones soften. A spinal curvature develops. The wrist, knee, and ankle joints enlarge. The muscles don't develop and there's a nervousness that cannot be relieved. This becomes a bone disorder called rickets.
In a growing infant, lack of vitamin D causes problems with tooth eruption and the teeth do not line up correctly.
In an adult, vitamin D deficiency is called osteomalacia. Vitamin D strengthens the teeth, preventing tooth decay and inflammation of the gums and tooth sockets.
Tetany, uncontrollable spasms in muscles, also results with a vitamin D deficiency accompanied by numbness and tingling.
A vitamin D deficiency may also cause nearsightedness. Recent studies have found a connection of colon, pancreatic, ovarian, prostate and breast cancer with vitamin D deficiency.
Recent research shows that vitamin D deficiency increases the risk of infections, especially for tuberculosis, flu and pneumonia. Low levels also increase risk of peripheral artery disease.
A Word of Warning
Vitamin D supplementation can be tricky. At the right dosage, vitamin D promotes the absorption of calcium for bone formation and mineralization. At very high levels, bone starts breaking down. If vitamin K is not adequate, Vitamin D triggers calcification of the soft tissues. Vitamin D is a pro-hormone; it is converted into a hormone 1, 25-D.
Hypervitaminosis D has occurred in manufacturing and industrial accidents. Too much sun exposure will never cause vitamin D toxicity because any excess is degraded in the body. Fish liver oil consumption has never produced an overdose either; however, there have been some reports of excess vitamin A taken with high doses of fish oil.
Synthetic forms can cause problems especially with levels that exceed 40,000 IU per day. Children should not take more than 2000 IU per day; adults 100,000 IU and infants 1000 IU.
Acute overdosage results in symptoms such as nausea, vomiting, diarrhea, dizziness, weariness, urinary frequency, and calcification of the heart, blood vessels and lungs. The symptoms reverse on their own in a few days after the dosage is stopped. If dosage is continued, renal failure can occur.
Taking too much vitamin D can result in calcium buildup in the arteries and kidneys, especially when not enough calcium and phosphorus is taken at the same time. All nutrients work together, and imbalances result whenever any one nutrient is taken by itself.
Excess vitamin D can also cause elevated blood pressure.
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1. Dunne, Lavon. Nutrition Almanac, McGraw-Hill Publishing, 2002.