Vitamin D is a steroid vitamin, a group of fat-soluble prohormones, which encourages the absorption and metabolism of calcium and phosphorous. People who are exposed to normal quantities of sunlight do not need vitamin D supplements because sunlight promotes sufficient vitamin D synthesis in the skin.
Five forms of vitamin D have been discovered, vitamin D1, D2, D3, D4, D5. The two forms that seem to matter to humans the most are vitamins D2 (ergocalciferol) and D3 (cholecalciferol).
Researchers at the University of Minnesota found that Vitamin D levels in the body at the start of a low-calorie diet predict weight loss success, suggesting a possible role for vitamin D in weight loss.
Data collected from the National Health and Nutrition Examination Survey (NHANES), USA found that 9% (7.6 million) of children across the USA, was vitamin D deficient (defined as less than 15 ng/mL of blood), while another 61 percent, or 50.8 million, was vitamin D insufficient (15 to 29 ng/mL) “We expected the prevalence of vitamin D deficiency would be high, but the magnitude of the problem nationwide was shocking,” says lead author Juhi Kumar, M.D., M.P.H., a fellow in pediatrics at Children’s Hospital at Montefiore Medical Center, The University Hospital and Academic Medical Center for Albert Einstein College of Medicine.
Vitamin D for humans is obtained from sun exposure, food and supplements. It is biologically inert and has to undergo two hydroxylation reactions to become active in the body. The active form of vitamin D in the body is called Calcitriol (1,25-Dihydroxycholecalciferol).
Calcitriol promotes the absorption of calcium and phosphorus from food in the gut and reabsorption of calcium in the kidneys – this increases the flow of calcium in the bloodstream. This is essential for the normal mineralization of bone and preventing hypocalcemic tetany. Hypocalcemic tetany is a low calcium condition in which the patient has overactive neurological reflexes, spasms of the hands and feet, cramps and spasms of the voice box (larynx). Calcitriol also plays a key role in the maintenance of many organ systems.
Various forms of vitamin D
We know about 5 forms of vitamin D, of which vitamins D2 and D3 are the major forms as far as humans are concerned. They are known collectively as calciferol.
- Vitamin D1, molecular compound of ergocalciferol with lumisterol.
- Vitamin D2, ergocalciferol (made from ergosterol).
It is produced by invertebrates (animals without a spine, vertebral column), fungus and plants in response to sunlight (UV irradiation). Humans and other vertebrates do not produce vitamin D2. We don’t know much about what vitamin D2 does in invertebrates. We know that ergosterol is a good absorber of ultraviolet radiation which can damage DNA, RNA and protein; consequently many scientists believe it may serve as a sunscreen that protects organisms from sunlight damage.
- Vitamin D3, cholecalciferol (made from 7-dehydrocholesterol).
Vitamin D3 is made in the skin when 7-dehydrocholesterol reacts with ultraviolet light at 270-300 nm wavelengths – peak vitamin D3 production occurs between 295-297 nm. It is only when the UV index is greater than 3 that these UVB wavelengths are present.
A UV index of more than 3 occurs every day in the tropics, every day during some of spring, all of summer, and parts of autumn in temperate areas, and hardly ever at all in the arctic circles. Temperate regions are all regions outside the tropics and arctic circles. The number of days of the year when the UV index is greater than 3 become fewer the further you move away from the tropics.
A human requires ten to fifteen minutes of sun exposure at least twice a week on the face, arms, hands, or back without sunscreen with a greater than 3 UV index for adequate amounts of vitamin D3. Longer exposure results in the extra vitamin supply being degraded as fast as it is generated.
- Vitamin D4, 22-dihydroergocalciferol.
- Vitamin D5, sitocalciferol (made from 7-dehydrositosterol).
Which is more important for humans, vitamins D2 or D3?
Both vitamins D2 and D3 are used in human nutritional supplements. Pharmaceutical forms include calcitriol (1alpha, 25-dihydroxycholecalciferol), doxercalciferol and calcipotriene. The majority of scientists state that D2 and D3 are equally effective in our bloodstream. However, some say that D3 is more effective. Animal experiments, specifically on rats, indicate that D2 is more effective than D3.
What do we need vitamin D for?
- It is crucial for the absorption and metabolism of calcium and phosphorous, which have various functions, especially the maintenance of healthy bones.
- It is an immune system regulator.
- It may be an important way to arm the immune system against disorders like the common cold, say scientists from the University of Colorado Denver School of Medicine, Massachusetts General Hospital and Children’s Hospital Boston.
- It may reduce the risk of developing multiple sclerosis. Multiple sclerosis is much less common the nearer you get to the tropics, where there is much more sunlight, according to Dennis Bourdette, chairman of the Department of Neurology and director of the Multiple Sclerosis and Neuroimmunology Center at Oregon Health and Science University, USA.
- Vitamin D may have a key role in helping the brain to keep working well in later life, according to a study of 3000 European men between the ages of 40 and 79.
- Vitamin D is probably linked to maintaining a healthy body weight, according to research carried out at the Medical College of Georgia, USA.
- It can reduce the severity and frequency of asthma symptoms, and also the likelihood of hospitalizations due to asthma, researchers from Harvard Medical School found after monitoring 616 children in Costa Rica.
- It has been shown to reduce the risk of developing rheumatoid arthritis in women.
- A form of vitamin D could be one of our body’s main protections against damage from low levels of radiation, say radiological experts from the New York City Department of Health and Mental Hygiene.
- Various studies have shown that people with adequate levels of vitamin D have a significantly lower risk of developing cancer, compared to people with lower levels. Vitamin D deficiency was found to be prevalent in cancer patients regardless of nutritional status, in a study carried out by Cancer Treatment Centers of America.
Sunlight and vitamin D requirements
If you live in the tropics and can expose your unprotected skin to two sessions of 15 minutes of sunlight each week your body will naturally produce adequate amounts of vitamin D. The following factors may reduce your body’s vitamin D synthesis:
- If you live far from the equator, your sunlight exposure will be less during many months of the year.
- Cloud cover
If your body cannot produce enough vitamin D because of insufficient sunlight exposure you will need to obtain it from foods and perhaps supplements. Experts say that people with a high risk of vitamin D deficiency should consume at least 25 μg (1000 IU) of vitamin D each day so that there is a good level of 25-hydroxyvitamin D in the bloodstream. Elderly people, as well as people with dark skin should consume extra vitamin D for good health.
The American Academy of Pediatrics recommends that exclusively or partially breastfed babies should receive supplements of 400 UI per day shortly after birth, and when they are weaned they should consume a minimum of 1,000 mL/day of vitamin D fortified formula or whole milk. Non-breastfed infants consuming less than 1,000 mL/day of vitamin D-fortified formula or milk should receive a vitamin D supplement of 400 IU per day. It also recommends that older children and adolescents who do not get 400 IU per day through vitamin D fortified milk and foods should take a 400 IU vitamin supplement each day.
Vitamin D and nutrition
Over the last few hundred years human lifestyles have changed. The industrial revolution resulted in more indoor work and less exposure to sunlight. Many societies around the world wore more clothing over the centuries, further reducing skin exposure to sunlight. These changes have brought with them a significant reduction in the natural production of vitamin D and subsequent diseases.
Countries responded to these changes by fortifying some foods with vitamins D2 and D3, examples include breakfast cereals, bread, pastries, oil spreads, margarine, milk and other dairy products. Initially, some scientists complained that nutritional fortification and recommended supplementation doses were not making up for the shortfall. These people were ignored, and sometimes ridiculed – however, over the last few years studies indicate that they may have been right after all.
Not that many foods contain vitamin D. Some fish, such as salmon, tuna and mackerel, as well as fish liver oils are considered to be the best sources. Some vitamin D is also present in beef liver, cheese and egg yolks. Most of these are Vitamin D3. Some mushrooms provide variable amounts of vitamin D2.
Most of the food sourced vitamin D in the western diet comes from fortified foods – where vitamin D is artificially added. Most US milk is fortified with 100 IU/cup of vitamin D. In the 1930s milk was fortified in many countries to combat rickets, which was a major health problem then.
What is vitamin D deficiency?
Vitamin D deficiency is when your body, more specifically your blood, does not have enough vitamin D. This can be caused by the following factors:
- Inadequate exposure to the right kind of sunlight
- Inadequate intake from foods and supplements
- Disorders in the gastrointestinal tract that limit absorption
- Liver disorders
- Kidney disorders
- Some hereditary disorders (very rare)
Vitamin D deficiency can lead to the following conditions and illnesses:
- Rickets – a disease of children and infants that interferes with normal bone formation – a failure to mineralize bone. Bones become distorted and bend wrongly because they are soft. During the first three decades of the 20th century rickets was mainly caused by lack of direct exposure to sunlight. The ultraviolet rays necessary for vitamin D synthesis do not pass through ordinary window glass.
- Osteomalacia – softening of the bone caused by demineralization (loss of mineral), mainly loss of calcium from bone. This disorder only affects adults and can cause severe musculoskeletal pain.
- Osteoporosis – reduced bone mineral density and increased bone fragility.
- Vitamin D deficiency has also been linked to the following diseases:
- Hypertension (high blood pressure)
- Heart failure, according to US researchers.
- Ischemic heart disease
- TB (tuberculosis)
- Periodontal disease
- MS (multiple sclerosis)
- Chronic pain
- SAD (seasonal affective disorder)
- Peripheral artery disease
- Cognitive impairment
- Cardiovascular disease among patients with diabetes
- Parkinson’s disease (possibly: we are not sure whether Parkinson’s causes low vitamin D levels, or whether low vitamin D causes Parkinson’s)
- Alzheimer’s disease, suspected by researchers from the Sunlight, Nutrition, and Health Research Center.
- Immune system problems – a University of Missouri nutritional sciences researcher found that vitamin D deficiency is associated with inflammation, a negative response of the immune system, in healthy women.
- Bacterial vaginosis – a common vaginal infection that increases a pregnant woman’s risk of preterm delivery, according to scientists at the University of Pittsburgh.
Mixed messages regarding sun exposure
For decades we have been told to stay out of the sun, to wear hats and cover ourselves with sun block to protect against skin cancer – and also significantly reducing our levels of vitamin D. Add to that a growingly sedentary lifestyle where we and our children spend more time indoors either watching TV or in front of a computer monitor, and it is not surprising that millions of people have excessively low levels of vitamin D in our system.
Then we are told that sunlight can rapidly make up for any vitamin D shortfall, while at the same time the American Academy of Dermatology continues to recommend that the public obtain vitamin D from nutritional sources and dietary supplements, and not from unprotected exposure to ultraviolet radiation because of the skin cancer risk, and we despair.
Telling people to get their vitamin D from just food and supplements obviously does not work. People have been told that for the last twenty years and vitamin D deficiency or insufficiency has increased significantly. It is estimated that 50% of American elderly women consume far less vitamin D in their diet than recommended. Consequently, vitamin D deficiency is a serious problem among the elderly in the USA.
It is understandable why a dermatologist, who is in direct contact with skin cancer patients, advises people to stay out of the sun. However, millions of people are and will develop other very serious diseases because their vitamin D levels are too low. Skin cancer is one factor, but there are many other factors.
Large studies are required that can clearly tell us:
1. Why is the current policy of telling people to get just their vitamin D from nutritional sources not working?
2. Is the current vitamin D problem greater than the skin cancer problem?
3. Is it possible to estimate what the impact of recommending 15 minutes twice a week of sun exposure would be on skin cancer numbers, and the health benefits from a resulting lower incidence of vitamin D deficiency in the population?
Some health authorities are starting to change their recommendations. Here is a quote from the Cancer Council, Australia (2009):
“Sun exposure is the cause of around 99% of non-melanoma skin cancers and 95% of melanomas in Australia. However, exposure to small amounts of sunlight is also essential to good health. A balance is required between avoiding an increase in the risk of skin cancer by excessive sun exposure and achieving enough exposure to maintain adequate vitamin D levels.”
Written by Christian Nordqvist
Copyright: Medical News Today