What is a vitamin?
Vitamins, like all minerals and essential amino acids, are compounds that are not produced naturally by the body and have to be either taken in the diet or synthesised internally. There are thirteen vitamins which get the suffix A, B, C, D, E and K. These are all essential for normal growth and development and most are found in our daily diets, There are two exceptions, firstly vitamin K which is produced by the gut flora and secondly vitamin D3 which is synthesised in the skin in the presence of sunlight. They are divided up into fat soluble vitamins which can be stored in the body and used when required such as vitamins A and D, and water soluble vitamins which are not stored in the body and thus must be taken more frequently such as vitamins B and C.
What is Vitamin D?
Vitamin D is required by the body and performs many functions, the most important of which is maintaining bone health. Only small amounts are present in food and certain foods are fortified with vitamin D. However the main source of Vitamin D is production in the skin during exposure to sunlight. In today’s society we don’t get as much sunlight as our ancestors through the increased use of sunscreens and lifestyles which mean that most of us spend more time indoors. Furthermore in the UK it is now well accepted that there is insufficient sunlight to produce the required levels of Vitamin D all year round This leaves us as a population at a higher risk of Vitamin D deficiency. (see the results of two recent studies below). Vitamin D is however a fat soluble vitamin which means that any surplus can be stored for long periods in the body for future use.
Dietary Vitamin D
As mentioned above very few natural foods contain Vitamin D. The highest levels are found in oily fish such as salmon, tuna, and mackerel, and fish liver oils such as cod liver oil. Smaller amounts of Vitamin D are found in other foods such as liver, cheese, and egg yolks.
Some foods are artificially fortified with Vitamin D, these include some breakfast cereals and margarine. All infant feeding formulas are fortified with Vitamin D, however it is important to note that human breast milk actually contains only very low levels.
Despite the presence of vitamin D in food there may not be enough to achieve the required amount (particularly for children under 5 years). For example one egg yolk contains only 1 microgram of Vitamin D. The Department of Health and the Chief Medical Officers recommend a dose of 7-8.5 micrograms (approx 300 units) for ALL children from 6 months to 5 years of age 1
Vitamin D Deficiency - At Risk Groups
The Department of Health describes several at risk groups, adults 65 years and older, people with dark skin and people with low sun exposure while younger at risk groups include pregnant or breastfeeding women, infants, adolescents and people suffering from malabsorbtion (e.g.coeliac disease), liver or kidney diseases.
What happens if I don’t have enough
Vitamin D deficiency is a serious medical condition with significant health consequences especially in children. Deficiency during periods of bone growth results in bone deformity known as rickets typically seen in early childhood. Rickets used to be common in poor and overcrowded city dwellers more than a century ago but, has become more common again in recent years2. Other symptoms–muscle weakness, delay in walking and bone pains may be a feature of less severely affected children. Recent research indicates that in many parts of the country the majority of children have a low level of Vitamin D.3
This increase in Vitamin D deficiency has been largely attributed to the fact that children are spending more time indoors, and when they are outdoors their skin is protected from the sunlight either by clothing or by widespread use of sunblock products. A new survey in 2014 has shown an increase in symptomatic Vitamin D deficiency in the UK population. Hospital admissions for Vitamin D deficiency and rickets, in the under-16s grew from 1,398 in 2009/10 to 4,638 in 2013/14.4
The principle need for Vitamin D in the body is in the regulation of calcium and phosphorus essential for bone health and normal dentition. If this balance is disturbed the circulating levels of calcium in the body changes. A reduction in the circulating levels of calcium triggers the body to break down calcium deposits in the bones and teeth to return the calcium levels to normal. This breakdown may lead to conditions such as rickets in children, which is traditionally seen as children with ‘bowed legs’ or ‘knock knees’, and in adults to osteomalacia, which is a softening of the bones giving rise to muscle weakness, bone pain and fragility fractures. In the early stages of this disease patients can have symptoms such as tiredness or general aches and pains.
- To increase the intake of Vitamin D and reach the recommended daily allowance all year round, dietary supplements are available, and are recommended by the NHS
- Dietary supplements containing Vitamin D are available in many forms and strengths. Your doctor, midwife or health-visitor will be able to advise. Vitamin D medicines (not food supplements) are available on prescription which have strictly controlled content which is vitally important to ensure safety of use in all patient groups
How is Vitamin D deficiency and insufficiency defined?
To quantify your Vitamin D status your doctor will take a blood sample and measure the serum concentration of 25-hydroxy Vitamin D (25-OHD). Depending on the levels detected the doctor will diagnose and categorise your Vitamin D status as outlined in the table below.
Only the most severe category necessarily gives rise to symptoms; whereas at levels that are not severely deficient, but nevertheless sub-optimal, or insufficient, symptoms are likely to be absent or mild.
If you feel you are at risk of deficiency or are getting insufficient amounts of Vitamin D you should consult your GP.
- Vitamin D – Advice on Supplements for At Risk Groups. Letter from the Chief Medical Officers for the United Kingdom. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/213703/dh_132508.pdf