Biology Sample Assignment Part 1

Physical activity when UV levels are above 3—is it safe for children to be outside?

The common question we are asked is 'When is it safe to let children outside to play'?

The answer is that children should be allowed outside to play throughout the day, provided that skin is well protected and shade facilities are available when the UV levels are 3 and above. It is important that extra care be taken during the middle of the day when UV is at its peak.

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We understand that rescheduling outside activities to earlier in the day or later in the afternoon, although preferable, is not always possible. It is important that physical activity opportunities for children are not missed- If the only time children can be outside is over the middle of the day. If this happens though, extra precautions with skin protection at this time are needed and may mean minimising time outside, using shade or indoor areas.

Once foods were fortified with vitamin d and rickets appeared to have been conquered, many health care.

Professionals thought the major health problems resulting from vitamin D deficiency had been resolved. However, rickets can be considered the tip of the vitamin D–deficiency iceberg. Vitamin D deficiency remains common in children and adults. In utero and during childhood, vitamin D deficiency can cause growth retardation and skeletal deformities and may increase the risk of hip fracture later in life. Vitamin D deficiency in adults can precipitate or exacerbate osteopenia and osteoporosis, cause osteomalacia and muscle weakness and increase the risk of fracture.

The discovery that most tissues and cells in the body have a vitamin D receptor and that several possess the enzymatic machinery to convert the primary circulating form of vitamin D, 25-hydroxyvitamin D, to the active form, 1,25-dihydroxyvitamin D, has provided new insights into the function of this vitamin. Of great interest is the role it can play in decreasing the risk of many chronic illnesses, including common cancers, autoimmune diseases, infectious diseases and cardiovascular disease. The nature of vitamin D deficiency, discuss its role in skeletal and nonskeletal health and suggest strategies for its prevention and treatment. Sources and Metabolism of Vitamin D Humans get vitamin D from exposure to sunlight, from their diet and from dietary supplements. A diet high in oily fish prevents vitamin D deficiency. Solar ultraviolet B radiation (wavelength, 290 to 315 nm) penetrates the skin and converts 7-dehydrocholesterol to previtamin D3, which is rapidly converted to vitamin D3. Because any excess previtamin D3 or vitamin D3 is destroyed by sunlight, excessive exposure to sunlight does not cause vitamin D3 intoxication. Few foods naturally contain or are fortified with vitamin D. The 'D' represents D2 or D3. Vitamin D2 is manufactured through the ultraviolet irradiation of ergosterol from yeast and vitamin D3 through the ultraviolet irradiation of 7-dehydrocholesterol from lanolin. Both are used in over-the-counter vitamin D supplements, but the form available by prescription in the United States is vitamin D2.

What Is Vitamin D And Why Is Important?

Vitamin D forms in the skin when it is exposed to UV from sunlight. Vitamin D can also be obtained in some foods, such as margarine and some dairy products fortified with vitamin D, as well as oily fish, eggs and liver. However the vitamin D in food makes a relatively small contribution to a person's overall vitamin D levels. We need vitamin D to maintain good health and to keep bones and muscles strong and healthy.

Treatment Of Vitamin D Deficiency

Vitamin D is stored in fat and muscle and is slowly released, particularly during winter. In vitamin D deficient patients, it is necessary to replete vitamin D stores. While the daily requirement for vitamin D is 400–600 IU per day, a much larger dose is used to treat vitamin D deficient patients. As vitamin D is fat soluble with a halflife >3 weeks, large doses are needed before changes in serum 25OHD are seen. High dosages of vitamin D (3000–5000 IU per day for 6–12 weeks [Ostelin]) may be used to replete body stores. Oral doses of 10 000 IU per day over 90 days have been shown to increase serum 25OHD levels to 86 nmol/L in postmenopausal women at latitude 34°S.23 Higher doses of 50 000–500 000 IU orally or 600 000 IU intramuscularly can effectively treat vitamin D deficiency, however, they are not currently available in Australia and there is the possibility of inducing hypercalcaemia/ hypercalciuria. Serum 25OHD levels should be checked at 3–4 monthly intervals to ensure adequacy of replacement. Calcitriol, the bioactive preparation of vitamin D, is not recommended for treating patients with simple vitamin D deficiency. This agent has a narrow therapeutic window and may result in significant hypercalcaemia. Moreover, changes in serum 25OHD levels are not a reflection of the calcitriol therapy.

What Can Be Done?


Those at high risk of Vitamin D deficiency should all be screened. This includes those who are dark skinned, women who are veiled and their children and those living in institutions or confined to the indoors. In infants most of the Vitamin D is acquired through maternal transfer, therefore Vitamin D deficiency in mothers is likely to have detrimental consequences for their infants.

Exposure To Sunlight:

People who are born with naturally dark skin (Type V or VI from the table below) require significant amounts of sun exposure to obtain Vitamin D in an amount equivalent to 1000 IU. This exposure needs to occur in peak ultraviolet periods between 10am and 3pm, 4 times per week between 20 and 30 mins April - September and up to 75 minutes in June and July in Perth. Times will vary in other parts of Australia. Sun protection should be used if exposure is likely tobe longer than the recommended times but for people who are truly dark skinned there should be no danger of sunburn. Sunscreen use does inhibit the production of Vitamin D.

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