Vitamin D Vitamin D is a fat-soluble vitamin that is perceived to not have any deficiency problems. This is because the typical Australian lifestyle provides ample Vitamin D concentrations. It is found in food, but can also be made in our bodies after exposure to ultraviolet rays from the sun.
The role of Vitamin D
The main role of Vitamin D is to regulate calcium and phosphorus levels in the blood. It is important for bone health and maintaining normal physiological function.
Vitamin D acts in the lining of the small intestine promoting the absorption of calcium. It also maintains calcium levels and allows controlled deposits of calcium and phosphorus into bones during growth. Without Vitamin D bones can become thin and brittle, as the calcium cannot be used.
What if you donít have enough?
The result of a deficiency in Vitamin D is rickets in young children and osteomalacia in adults. These conditions result in misshapen bones that are easily fractured. In adults it can also lead to muscular weakness. These conditions may occur when intake is inadequate or exposure to sunlight is limited. It may also occur in someone who cannot absorb vitamin D, or if the kidneys cannot convert vitamin D to its active form.
Who is most at risk of deficiency and may need extra vitamin D?
- They may have a reduced ability to convert Vitamin D from the skin with the aid of sunlight to its active form.
- The kidneys may have a reduced capacity to perform this function.
Individuals with reduced exposure to sunlight.
- Women covering up for religious reasons
- Young children to protect against sun
- Teenagers choosing indoor games and activities eg computers and TV
Individuals with darker skin
- May have reduced absorption
- May have reduced exposure- perceive lighter skin is desirable.
Individuals who have reduced ability to absorb dietary fat and therefore the fat soluble Vitamin D.
- Crohnís disease, cystic fibrosis or other small bowel disease
- Chronic diarrhoea
- Short bowel syndrome
- Fat malabsorption through medication eg Xenical, Obix or Questran.
A simple blood test can detect the presence of a deficiency.
It is generally recommended that you should consume 10mcg per day of vitamin D and have 2 hours per week exposure to sunlight.
What are the sources of Vitamin D?
Only a few foods contain significant amounts of vitamin D. These include fatty fish and fish oils. Margarines are sometimes enriched.
|Best food sources||Ķg*|
|Cod liver oil, 20 mL||42|
There are 1,000,000 Ķg in one gram
Exposure to sunlight
Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight commences vitamin D synthesis in the skin. It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diet.To obtain sufficient sun exposure without increasing your risk of skin cancer, avoid peak summer times from 10am to 3 pm. The cancer council recommends that you use protection against the sun; shade, hats, clothing, sunglasses and sunscreen during this time. During summer time, 2 to 14 minutes (exposing 15% of the body) before 10am and after 3pm three to four times per week. Between October to March, 10 to 15 minutes (exposing the face, arms and hands) before 10am and after 3pm three to four times per week. These recommendations only apply to fair skinned people. Darker skinned people need around six times more exposure to produce as much Vitamin D. Those with dark skin, or who have limited sun exposure, may benefit from a vitamin D supplement and should discuss this with their dietitian.
Five times the recommended dose of vitamin D (50mcg) can be harmful. It can cause nausea, vomiting, constipation, weakness and weight loss. Too much calcium can be absorbed and lead to calcification of the soft tissues. This can also lead to changes in mental state.
This is only likely to occur with regular pharmacological doses of vitamin D such as daily cod liver oil intake.
UV light and skin cancer
WARNING: UV light also causes skin cancer so doesnít rush out to soak up some of the sunís rays. A small amount of sun around 20 minutes a day is sufficient, but donít forget the sunscreen.
Current Issues and Controversies About Vitamin D
Vitamin D and osteoporosis
It is estimated that over 25 million adults in the United States have, or are at risk of developing osteoporosis. Osteoporosis is a disease characterized by fragile bones. It results in increased risk of bone fractures. Having normal storage levels of vitamin D in your body helps keep your bones strong and may help prevent osteoporosis in elderly, non-ambulatory individuals, in post-menopausal women, and in individuals on chronic steroid therapy.
Researchers know that normal bone is constantly being remodeled (broken down and rebuilt). During menopause, the balance between these two systems is upset, resulting in more bone being broken down (reabsorbed into the blood stream) than rebuilt. Estrogen replacement, which limits symptoms of menopause, can help slow down the development of osteoporosis by stimulating the activity of cells that rebuild bone.
Vitamin D deficiency, which occurs more often in post-menopausal women and older Americans, has been associated with greater incidence of hip fractures. A greater vitamin D intake from diet and supplements has been associated with less bone loss in older women. Since bone loss increases the risk of fractures, vitamin D supplementation may help prevent fractures resulting from osteoporosis.
In a group of women with osteoporosis hospitalized for hip fractures, 50% were found to have signs of vitamin D deficiency. Treatment of vitamin D deficiency can result in decreased incidence of hip fractures, and daily supplementation with 800 IU (20 micrograms) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D. Your physician will discuss your need for vitamin D supplementation as part of an overall plan to prevent and/or treat osteoporosis when indicated.
Vitamin D and cancer
Laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers. Some dietary surveys have associated increased intake of dairy foods with decreased incidence of colon cancer. Another dietary survey associated a higher calcium and vitamin D intake with a lower incidence of colon cancer. Another recent study of cancer, revealed the less sunlight subjects received, the more likely it was that they would die of cancer. The strongest correlation was found with breast, colon and ovarian cancers. The protective effect is understood to be Vitamin D. It promotes normal cell growth and maturation. Too little may allow cells with mutations to replicate and become cancers. Risk increases with age as the skinís ability to manufacture vitamin D decreases. Well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D supplements is protective against some cancers. Until such trials are conducted, it is premature to advise anyone to take vitamin D.
Vitamin D and steroids
Corticosteroid medications are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for a person's medical treatment, but they have potential side effects, including decreased calcium absorption. There is some evidence that steroids may also impair vitamin D metabolism, further contributing to the loss of bone and development of osteoporosis associated with steroid medications. For these reasons, individuals on chronic steroid therapy should consult with their physician or an accredited dietitian (APD) about the need to increase vitamin D intake through diet and/or dietary supplements.
Vitamin D and Alzheimer's Disease
Adults with Alzheimer's disease have increased risk of hip fractures. This may be because many Alzheimer's patients are homebound, and frequently sunlight deprived. Alzheimer's disease is more prevalent in older populations, so the fact that the ability of skin to convert vitamin D to its active form decreases as we age also may contribute to increased risk of hip fractures in this group. One study of women with Alzheimer's disease found that decreased bone mineral density was associated with a low intake of vitamin D and inadequate sunlight exposure. Physicians evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer's disease.
Added to site on : Thursday, 10 October 2002