Why do we need vitamin D?

Vitamin D is needed for the development and growth of bone – it promotes calcium absorption, helping to keep bones and teeth strong. Vitamin D also has other functions in the body, including a role in cellular differentiation and proliferation, glucose homeostasis and immune regulation.

What are common sources of vitamin D?

Vitamin D is produced in the body via exposure to sunlight – UVB radiation on uncovered skin allows cutaneous production of vitamin D through a series of biochemical pathways. Very few foods in nature contain vitamin D. Salmon, tuna, mackerel and fish liver oils are among the best sources. Small amounts of vitamin D are found in beef, liver, cheese, and egg yolks. Fortified foods, such as milk and ready-to-eat breakfast cereals, provide vitamin D.

Is daily sun exposure enough to ensure adequate vitamin D status?

Vitamin D production via sun exposure on skin is a major source of vitamin D, but cutaneous production depends on location and season. People who live in countries close to the equator synthesize vitamin D throughout the year; however, the further North or South of the equator one travels the less influence the sun has on vitamin D synthesis. During the winter months (October-April) in more northern countries (i.e. Ireland) there is minimal cutaneous vitamin D production, so the entire population,including infants, are dependent on dietary sources of vitamin D to ensure adequate concentrations in the blood. Sunscreen reduces vitamin D production in the skin because UVB rays are prevented from penetrating the skin. Other factors that affect cutaneous vitamin D production are skin colour (the darker the skin the less vitamin D produced) and clothing habits. In Ireland and other European countries, national dietary surveys have shown low intakes of vitamin D; therefore, supplementation and fortification policies may be a solution to prevent low vitamin D status.

Is it necessary to give exclusively breastfed infants a vitamin D supplement?

Breastfeeding is recommended for at least the first six months of life, as it is the best form of food for a developing and growing baby. Breast milk contains many essential nutrients and immunological agents that promote the development of a baby’s immune system. Unfortunately, breast milk is a poor source of vitamin D, especially if the mother herself has a low vitamin D status, so supplementation of exclusively breastfed infants should be promoted.

How will I know if my baby or child has rickets due to vitamin D deficiency?

Rickets is not easily diagnosed in an infant who has not yet begun to walk. It is a disease of the bones and an x-ray is used to diagnose the condition. When a child suffering from rickets walks, excessive bowing of the legs is evident, in addition to swelling of the wrists and ankles. Infants with vitamin D deficiency have a slow growth rate and some may suffer from breathing and heart problems.

Why do women have a higher incidence of osteoporosis than men?

It is well known that the incidence of osteoporosis is higher in women than men, with 1 in 3 women and 1 in 5 men affected by this condition. A key reason for the gender difference in the incidence of osteoporosis may be due to the fact that the rate of bone loss is higher in postmenopausal women as a result of declining oestrogen levels.


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