Frequently Asked Questions
Why do we need vitamin D?
Vitamin D is needed for the development and growth of bone – it promotes calcium absorption, helping to keep bone and teeth strong. Vitamin D also has other functions in the body, including cellular differentiation and proliferation, glucose control 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 converts to vitamin D through 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.
What are current recommendations for vitamin D?
In Ireland, the RDA for vitamin D is 0-10µg, depending on how much sunlight you obtain. In America, however, the adequate intake (AI) is 5µg/day.
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 synthesise vitamin D throughout the year; however, the further North or South of the equator you travel 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.
Do I need to give vitamin D supplements to infants who are fed infant formula?
No - in Ireland, infant formulas are already fortified with vitamin D. The average vitamin D content per 100ml for infant formula is 1.3µg and for follow-on formula is 1.5µg. All infants aged 0-12 months would benefit from having extra vitamin D as foods containing vitamin D are rarely included in weaning diets.
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 diagnoses the condition. When a child suffering from rickets walks, there is excessive bowing of the legs accompanied by 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. Key reasons for the gender difference in osteoporosis incidence may be due to the fact that the rate of bone loss is higher in postmenopausal women due to declining in oestrogen levels.
Should vitamin D supplementation be recommended in elderly adults?
Sunlight is a major source of vitamin D; however, since Ireland is situated between latitude 51 and 55 ºN, negligible cutaneous synthesis of vitamin D occurs between October and March. In addition, cutaneous synthesis of vitamin D decreases with age. The Food and Nutrition Board, Institute of Medicine (1997) suggests a daily vitamin D intake of 10µg for adults aged 51-70 years. A recent Irish study found that 89% of 51-64 year olds do not achieve the 10µg/day recommendation, with mean daily intakes (MDI) of vitamin D from food sources being 4.01 µg in men and 3.39 µg in women (Hill et al, 2004). Results from other studies (Hill et al, 2002, 2003 and Andersen et al, 2003 ) observed low vitamin D status in 50-75 year old Irish women between late winter and early spring. These findings indicate that dietary intake of vitamin D is not sufficient in Ireland to reach recommendations for the elderly population and vitamin D supplementation should be promoted among this population group.