The Vitamin D Story
Vitamin D and its production in the skin and food by sunlight was discovered in 1919-1924. This discovery led to the elimination of rickets, a condition caused by severe vitamin D deficiency (1).
Today vitamin D plays a crucial role in bone health by helping to absorb and utilise calcium in the body, without vitamin D it is thought we absorb no more than 15% of the calcium we consume (2).
Emerging science is indicating a role for vitamin D in a number of health outcomes including cardiovascular disease, immune function, diabetes and some cancers but further research is required to understand these links (2,3).
Vitamin D is known as the ‘sunshine vitamin’ because it is mainly produced through the action of sunshine on our skin. Vitamin D is also naturally found in a few foods such as oily fish, egg yolks and liver.
Vitamin D – Recommended Daily Allowance (RDA)
Recommended Daily Allowance is the level of intake of a nutrient on the basis of scientific knowledge thought to meet the needs of most of the population.
Table illustrating the Recommended Dietary Allowances for Vitamin D (µg)
(FSAI, 1999)
| Children | Early Adolescence | Adolescence | Adults | Elderly | Pregnancy & Breastfeeding | |||
|---|---|---|---|---|---|---|---|---|
| Age | 1-3 | 4-6 | 7-10 | 11-14 | 15-17 | 18-64 | 65+ | |
| Vit D µg | 10 | 0-10 | 0-10 | 0-15 | 0-15 | 0-10 | 10 | 10 |
The RDA for some age groups is based on a range, rather than a single amount as it was thought these age groups would receive adequate sunlight, and dietary intake was not considered necessary. However, experts are calling for the RDA of vitamin D to be reviewed as evidence is mounting to suggest we aren’t getting enough vitamin D from the sun (4,5).
In Ireland 74% of adults and 88% of primary school children had an average daily intake of vitamin D that was less than half of the RDA range of 5µg (6,7).
A study conducted in healthy adults in Ireland demonstrated that the vitamin D tissue stores developed during the production of vitamin D on the skin during the summer months were not enough to maintain adequate levels of vitamin D in the body through the winter (4).
The two main reasons for the low levels of vitamin D are the lack of sunshine in Ireland and the fact that only a few foods naturally contain vitamin D.
- Due to Ireland’s northerly latitude (51-55°N) very little UV light reaches the country between October and March (6 months) resulting in very little skin production of vitamin D. The vitamin D stores we make in summer have to last through winter and it has been suggested these stores are not sufficient (4).
- Very few foods frequently consumed naturally contain vitamin D, herring, kippers, mackerel and fish liver oils are among the best sources.
Vitamin D is important for all age groups.
Infants (0-12 months)
Adequate vitamin D intake in the first 12 months of life is vital for the healthy development of the skeletal system. The Food Safety Authority of Ireland (FSAI), assembled a Working Group of scientists and health professionals to address vitamin D intakes in infants in 2007. The outcome of the Working Group was the recommendation that all infants (0-12months) in Ireland should be supplemented with (5µg) vitamin D daily (8).
Children and adolescence
Adequate vitamin D and calcium intake during childhood and adolescence is crucial, as this is when the foundations of skeletal health are laid down, helping to reduce the risk of osteoporosis in later life (9). The RDA range for vitamin D broadens from 0-10 µg in children to 0-15 µg during adolescence as the pubertal growth spurt places higher demands on skeletal development.
Adults
It is thought that one of the key ways to achieve better bone health throughout life is to attain the highest possible peak bone mass which is normally achieved around the second decade of life. Even though genetics play a big part in peak bone mass, adequate vitamin D and calcium intake along with weight bearing activities can make an important contribution (9).
Osteoporosis is a condition which affects 1 in 3 women and 1 in 5 men and although genetics plays a big part in the risk of suffering from osteoporosis, achieving the highest possible peak bone mass is thought to play an important role in reducing the risk (9).
Elderly
Low vitamin D intake is common in the elderly, particularly those who are housebound or institutionalised. The RDA for vitamin D is 10µg as the ability to produce vitamin D on the skin decreases with age. Studies have shown vitamin D supplementation in elderly people with low intakes may help reduce fall frequency, risk of minimal trauma fractures and improve muscle strength in frail elderly (10).
Pregnancy and lactation
The RDA for vitamin D during pregnancy and lactation is 10 µg per day to meet the demands of the growing infant. As low levels of vitamin D during pregnancy are associated with poor vitamin D levels in the infant it is important for pregnant women to ensure adequate vitamin D intakes during pregnancy.
1. Deluca HF. (1988) The Vitamin D story. FASEB J (2): 224-236.
2. Holick MF. Vitamin D deficiency. N Engl J Med (2007) 357 (3): 266-281.
3. Holick, MF. Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. American Journal of Clinical Nutrition, (2004) 80 (suppl): 1678S-88S.
4. Cashman et al. Estimation of the dietary requirements for vitamin D in healthy adults. American Journal of Clinical Nutrition. (2008) 88 (6): 1535-1542.
5. Vieth et al. The urgent need to recommend an intake of vitamin D that is effective. American Journal of Clinical Nutrition. (2007) 85 (3): 649-650.
6. Hill et al. Vitamin D intakes in 18–64-y-old Irish adults. European Journal of Clinical Nutrition (2004) 58, 1509–1517.
7. Kiely et al. Irish Universities Nutrition Alliance. (2005). National Children’s Food Survey.
8. Food Safety Authority of Ireland (2007) Recommendation for a National Policy on Vitamin D Supplementation for Infants in Ireland.
9. Heaney et al. Peak Bone Mass. Osteoporosis International. (2000) 11:985-1009.
10. Bischoff-Ferrari HA, Willett WC, Wong JB, Giovannucci E, Dietrich T, Dawson-Hughes B (2005) Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. Journal of the American Medical Association 293, 2257-2264.