Jill Sommerville outlines the importance of vitamin D in the diet and looks at why the population in Ireland is particularly at risk of deficiency
Most people think of rickets as a disease of poor, developing countries. However, a number of years ago a group of dietitians in Ireland were surprised when they began to see the re-emergence of rickets in their clinical practices.
They were aware that rickets had essentially been eradicated at the end of World War II and they quickly brought their observations to the attention of the relevant authorities.
A subsequent study (2006) carried out in two major Dublin paediatric hospitals identified 20 cases of rickets and, according to the study’s authors, this is thought to be only ‘the tip of the iceberg’.
Rickets is caused by a deficiency in vitamin D in early infancy and childhood. One of the fat-soluble vitamins, vitamin D plays a major role in regulating calcium absorption, is essential for good bone health from conception and is involved in calcium metabolism, which forms strong bones.
Low levels of vitamin D trigger an increased rate of bone breakdown and increase the risk of osteoporosis in adults and of rickets in children.
In M O’Sullivan’s study of 70 healthy Irish adults, she showed 51 per cent had vitamin D insufficiency. Other studies on the vitamin D status of other groups of the population have all highlighted low vitamin D status and low vitamin D intakes.
A simple blood test to measure serum 25 hydroxyvitamin D (25-OH D) is the biomarker used to assess vitamin D status. Different experts recommend different cut-off points in order to establish deficiency and insufficiency.
The primary source of vitamin D is a natural process of sunlight acting on the skin to produce vitamin D in the body.
There are a small number of foods that contain vitamin D, but sunlight is the population’s main source.
As our knowledge of the dangers of skin cancer advances, more people are protecting their skin from the harmful effects of the sun, using sun block and other forms of sun protection. Naturally, this means that skin is not exposed sufficiently to the sun’s rays to produce adequate quantities of vitamin D. In Ireland, particularly with our northerly latitude, this means that we are unable to produce as much vitamin D naturally as our Mediterranean counterparts.
In addition, dark-skinned people and people who cover up for cultural reasons are at higher risk of vitamin D deficiency. In Ireland, rickets has tended to be identified in infants with dark skin. Naturally, it is not recommended to expose at-risk infants to the sun, hence the need for a daily vitamin D supplement.
Countries such as the UK and Canada, on similar latitudes to us, identified the problem of natural vitamin D deficiencies due to lack of natural sunlight many years ago. Health bodies and health professionals quickly implemented vitamin D supplementation programmes, which are constantly under review to provide best practice recommendations on supplementation doses to the appropriate populations.
In Ireland we are working on implementing these important supplementation programmes. To date, agreement has only been reached on supplementing babies aged 0-12 months and the Food Safety Authority of Ireland (FSAI) is recommending a policy of 200 IU (international units) daily.
Most other developed countries are using double that amount. It is vital that the new policy is communicated to parents, especially the parents of infants. From speaking to parents of newborn infants, it would appear that the Irish message of supplementing infants 0-12 months with 200 IU vitamin D3 daily appears to be slow in getting to all parents.
Crucial first year
The first year of life is critical for bone development. The dietary sources of vitamin D – which include oily fish, liver, egg yolks, some fortified cereals and margarine – do not form a regular part of an infant’s diet in Ireland. The FSAI recommends that regardless of the method of feeding, infants are at risk of having insufficient vitamin D stores, and that all infants would benefit from vitamin D supplementation.
Many healthcare professionals, especially nutritionists and dietitians, believe the population as a whole could also benefit from a vitamin D supplement. Whilst we are now aware of the population groups at risk of vitamin D deficiency, action could be taken to improve the advice on supplementation and hence improve future bone health and reduce the health costs associated with osteoporosis.
- Jill Sommerville, BSc, Human Nutrition & Dietetics, MSc Nutrition, Nutrition Manager, Pfizer Nutrition.
References on request.