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Vitamin D and sunlight

Introduction

Vitamin D is a fat-soluble vitamin. Two major forms of vitamin D are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized in plant and fungus. Vitamin D3, on the other hand can be synthesized in humans’ skin when it is exposed to ultraviolet B (UVB) rays from the sun. Hence, vitamin D is also widely known as the “sunshine” vitamin.

Sunlight As A Source Of Vitamin D

Vitamin D is not found in significant amounts in foods. Examples of food that contain vitamin D are fatty fishes (e.g. salmon, tuna), fish liver oils, beef liver, egg yolks and mushrooms. Most people therefore depend on exposure to the sun to satisfy their vitamin D requirements, which is free and easily available. UVB radiation with a wavelength of 290–320 nanometers from the sun penetrates uncovered skin and converts provitamin D3 in the skin to vitamin D3 (Institute of Medicine [IOM], 2010).

It has been suggested that approximately 5–30 minutes of sun exposure between 10.00 am and 3.00 pm at least twice a week to the face, arms, legs, or back without sunscreen will usually provide sufficient daily vitamin D requirements (Holick, 2007).

The ultraviolet rays that promote vitamin D synthesis in the skin can be blocked by heavy clouds and shade, including that produced by severe pollution. Exposure to sunshine indoors through a window does not produce vitamin D because UVB radiation cannot penetrate glass. Therefore, individuals who have less outdoor activity have to ensure adequate intake of vitamin D from other sources such as from the diet or by consuming health supplement products. Fortified foods such as dairy products (e.g. milk, cheese, and butter) with vitamin D are some major sources found in the diet.

The pigments of dark skin people provide some protection from the sun, but they also reduce vitamin D synthesis. Therefore, darker-skinned Individuals may need more sun exposure than lighter-skinned individuals to maintain an optimal vitamin D level.

Roles Of Vitamin D: Helps In Calcium Absorption And Prevention Of Osteoporosis

Vitamin D plays an important role together with calcium in the development and maintenance of bones and teeth. Calcium is the most abundant mineral found in the human body and 99% of the body’s calcium is stored in bones and teeth, which contribute to its strength. Vitamin D increases the absorption of calcium in the intestine and helps to maintain adequate calcium and phosphate concentrations in blood, which in turn contributes to the normal formation (mineralization) of bone (IOM, 2010).

Our bones undergo continuous remodeling via resorption and deposition of calcium into new bone and this balance changes with age. Bone breakdown may exceed formation of bones in elderly, especially in postmenopausal women due to decreased amounts of estrogen. The lack of estrogen increases bone resorption and decreases the deposition of calcium into new bone. This may consequently increase the risk of osteoporosis over time (IOM, 2010).

Vitamin D and calcium plays a crucial role in the prevention of osteoporosis. Osteoporosis is a disease in which the bone becomes weak and fragile and more likely to break (fracture). It is also known as a “silent disease” because there are typically no symptoms in the early stages of bone loss. Signs and symptoms such as back pain, stooped posture, loss of height or breaking of bones more easily than expected (e.g. when falling down or with minor injuries) may happen after the bones has been weakened due to disease progression.

Bone breakdown may also happen when calcium intake is insufficient or when the ingested calcium is poorly absorbed in the body causing the body to use its stored calcium to maintain normal biological functions. Therefore, insufficient intake of vitamin D may eventually lead to osteoporosis due to the decrease in calcium absorption (Heaney, 2003). Adequate daily intake of vitamin D and calcium as part of healthy diet together with regular exercise may reduce the risk of developing osteoporosis in later life (U.S. Food and Drug Administration [USFDA], 2008).

The other factors that increase the risk of developing osteoporosis are being female, thin, inactive, or of advanced age; smoking; drinking excessive amounts of alcohol; and having a family history of osteoporosis.

Vitamin D Deficiency And The Recommended Daily Intake

Vitamin D deficiency is manifested as rickets in children and osteomalacia in adults, which are the softening and weakening of bones due to insufficient deposition of calcium and phosphate into the bone matrix. Adequate daily intake of vitamin D is crucial to avoid complications from vitamin D deficiency. According to the National Coordinating Committee on Food and Nutrition (NCCFN), Ministry of Health Malaysia (2005, p. 129), the Recommended Nutrient Intakes (RNI) for various age groups are as follows:

Age Groups
RNI (µg/day)
RNI (IU/day)
Infants
0 – 5 months
6 – 11 months
5
5
200IU
200IU
Children
1 – 3 years
4 – 6 years
7 – 9 years
5
5
5
200IU
200IU
200IU
Boys
10 – 18 years
5 200IU
Girls
10 – 18 years
5 200IU
Men
19 – 50 years
51 – 65 years
> 65 years
5
10
15
200IU
400IU
600IU
Women
19 – 50 years
51 – 65 years
> 65 years
5
10
15
200IU
400IU
600IU
Pregnancy 5 200IU
Lactation 5 200IU

Conclusion

Vitamin D can be obtained easily from sunlight exposure to but this can be limited by environmental factors, genetic factors and lifestyle. Vitamin D from the diet may not be sufficient to meet the daily requirement of normal individuals. Taking health supplement products with an adequate amount of vitamin D required for the particular age group may help in maintaining an optimal vitamin D level. Should you have any health problems or if you are taking any other medications/ herbal products/ health supplement products, please consult a doctor or pharmacist before taking a vitamin D supplement.

References

  1. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  2. National Coordinating Committee on Food and Nutrition (2005).Recommended Nutrient Intakes for Malaysia. Putrajaya: Ministry of Health Malaysia.
  3. Holick, M.F. (2007). Vitamin D deficiency.New England Journalof Medicine, 357, 266-81.
  4. Heaney R.P. (2003). Long-latency deficiency disease: insights from calcium and vitamin D. American Journal of Clinical Nutrition,78, 912-9.
  5. U.S. Food and Drug Administration (2008).Food Labeling: Health Claims; Calcium and Osteoporosis, and Calcium, Vitamin D, and Osteoporosis
Last Reviewed : 06 June 2014
Writer : Ravin Chin a/l Thillainathan
Accreditor : Datin Shantini Thevanderan