Vitamin D deficiency remains a hot topic and GPs can play a vital role in ensuring the patient population meets the recommended levels
Author: Judy More, Paediatric Dietician and Registered Nutritionist Director, Child-nutrition.co.uk Ltd, Honorary lecturer, Plymouth University
New proposed vitamin D recommendations
Currently vitamin D supplements for preventing deficiency are only recommended for at risk groups (Table 1). But last year the Scientific Advisory Committee on Nutrition (SACN) completed a review of the evidence and the prevalence of vitamin D deficiency among the general population in the UK, and subsequently proposed a Recommended Nutrient Intake (RNI) of 10µg/day for the whole population over 12 months of age (SACN, 2015).1
When these recommendations are finalised in the next few months and sent to the Department of Health, policy will probably change to a recommendation of a supplement of 10µg/day for the whole population over 1 year of age. For infants an intake of 8.5-10 µg/day is likely to be recommended. This would mean a supplement from birth for breastfed infants as breastmilk does not contain this amount.
Why are supplements necessary for the general population?
In the UK a healthy, balanced diet provides all the nutrients needed except vitamin D, as few foods naturally contain it. Only oily fish is a significant source, while egg yolks, meat and a few fortified foods provide small amounts. Other foods contain no vitamin D or negligible amounts and most of the population consume less than 3µg of vitamin D per day.2
Fortified foods in the UK include:
- Margarine – fortification has been a legal requirement since World War II
- Formula milks – infant formulas, follow-on formulas and growing up milks
- Fortified milks – evaporated milk and fortified milks for toddlers e.g. Arla Big milk
- A few breakfast cereals
- Some brands of yogurts.
In other countries, such as Finland, Canada and the USA, a wider range of commonly consumed foods are fortified with vitamin D, such as fresh cows’ milk, other dairy products and some fruit juices.
Breast milk is low in vitamin D, and young infants depend on their fetal stores of vitamin D laid down during pregnancy. Hypocalcaemic seizures and tetany early in life, although rare, results from low fetal stores due to maternal vitamin D deficiency.
Dermal synthesis of pre-vitamin D is the main source of vitamin D, but is unreliable in the UK. Light of the critical wavelength for synthesis cannot pass through glass and the ideal time to spend outside each day is not easy to define as synthesis depends on:
- Season – sunlight of the critical wave length only reaches the UK between April and September. It is absorbed by the atmosphere during winter months.
- Latitude – in the south of the UK there is more sunlight of the critical wavelength than the north.
- Weather – more vitamin D can be synthesised on bright sunny days than on cloudy days.
- Air pollution – reduces the critical UV light waves available for skin synthesis.
- Time of day – more vitamin D is synthesised when sunlight is most intense in the middle of the day compared to early morning and late afternoon.
- Colour of skin – darker skins require more time in the sun to synthesise the same amount of vitamin D as light skins.3 Those of Asian, African and Middle Eastern ethnic origin are more likely to have lower vitamin D levels than Caucasians.
- Lifestyle – time spent outside with bare skin exposed facilitates vitamin D synthesis, which is greatly diminished when most skin is covered by clothes, as can be the fashion or in the case in girls and women with certain religious and cultural traditions.
- Sunscreen use – It blocks dermal synthesis of vitamin D.
Vitamin D excess as a result of excessive sunshine exposure does not occur as synthesis is inhibited when sufficient levels are achieved.4
Vitamin D deficiency in the UK
Low serum levels of vitamin D are found in significant numbers of all population groups in the UK: in winter 30-40% of all age groups in the general population are classed as vitamin D deficient. Even towards the end of summer 8% of adults and 13% of adolescents remain deficient.2
Deficiency is usually accompanied by normal blood levels for calcium and phosphorus, highnormal or elevated levels of parathyroid hormone (PTH), normal to elevated levels of total alkaline phosphatase, a low 24-hour urine calcium excretion rate, and low levels of total 25(OH)D. Patients with severe and long-standing vitamin D deficiency may present with overt hypocalcemia and/or hypophosphatemia, but this is the exception.
Consequences of vitamin D deficiency
The role of vitamin D in bone health is well defined; it promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and teeth and to prevent hypocalcaemic tetany. It is also needed for bone growth and bone remodelling by osteoblasts and osteoclasts.4 Without sufficient vitamin D, bones can become thin, brittle or misshapen and clinical manifestations are:
- Hypocalcaemic seizures due to low blood calcium levels – seen in young infants as a result of maternal vitamin D deficiency during pregnancy
- Rickets in growing children
- Osteomalacia in adults
- Osteoporosis in older adults.
Other roles of vitamin D are less well defined but epidemiological evidence strongly suggests it plays a role in growth, muscle strength, prevention of falls in the elderly and in decreasing the risk of cardiovascular disease, inflammatory and autoimmune diseases, some cancers and other chronic diseases1,4 such as:
- Type 1 and 2 diabetes
- Upper respiratory tract infections and wheeze including asthma
- Infectious diseases
- Multiple sclerosis
- Rheumatoid arthritis
Low vitamin D levels are also associated with severe pre-eclampsia in pregnant women.5,6
Vitamin D: vitamin or hormone?
The ultraviolet rays of wave length 290-315nm convert 7-dehydrocholesterol in the skin to previtamin D. This is metabolized in the liver to 25-hydroxyvitamin D (calcidol), which is a stable metabolite with a half-life of 2-3 weeks. It is converted in the kidney and select other tissues by the action of the 1á-hydroxylase enzyme to 1,25-di-hydroxyvitamin D (calcitriol), the active form which interacts with vitamin D receptors found in all cells. Hence, vitamin D could be more accurately called a steroid hormone.
It is fat-soluble and stored in adipose tissue or fat deposits when dermal synthesis and dietary intakes exceed daily requirements. Stores are used during the winter months when the critical wavelength in sunlight is insufficient for dermal synthesis.
The skin cancer vs dermal vitamin D synthesis debate
Concern over the balance between having sufficient sun exposure to produce vitamin D, and over-exposure leading to burning of the skin and an increased risk of skin cancer, has led to confusion of public health messages. To provide balanced, evidence-based advice a consensus statement on vitamin D was produced by several organisations with concerns in this area,7 which NICE has endorsed in its latest guidance NG34 Sunlight exposure: risks and benefits.8
Current recommendations on supplementation for at risk populations
Dietary recommendations for vitamin D intake for children over three years of age and most adults were not set in 1991, as it was expected that dermal synthesis of vitamin D would suffice. However, the National Diet and Nutrition surveys (NDNS) show that few at risk population groups in the UK meet their RNI for vitamin D through food alone, and will only attain their dietary RNI when taking a vitamin D supplement.2
In addition, other groups who are defined as at risk of vitamin D deficiency due to certain clinical conditions are children and adults who:
- are obese
- have gastrointestinal malabsorption
- have kidney or liver disease
- are on certain medications, such as statins.
Preventing vitamin D deficiency
The recommendations in NICE Public Health Guidance 56 Vitamin D: increasing supplement use among at-risk group, published in 2014, which specifically apply to CCGs, GP practice staff and local authorities are to:
- Ensure all health professionals recommend vitamin D supplements
- Increase access to vitamin D supplements
- Increase local availability of vitamin D supplements for at-risk groups
- Improve access to Healthy Start supplements (which could include GP practices stocking and distributing them either from the practice or a nearby pharmacy)
- Only test vitamin D status if someone has symptoms of deficiency or is at very high risk
- Raise awareness among health, social care and other relevant practitioners of the importance of vitamin D
- Raise awareness of the importance of vitamin D supplements among the local population
- Monitor and evaluate the provision and uptake of vitamin D supplements
- Develop national activities to increase awareness about vitamin D
- Ensure a consistent multiagency approach.11
Vitamin D supplements for prevention of vitamin D deficiency
The two main forms of vitamin D are:
- Vitamin D3 (cholecalciferol) produced by dermal synthesis and provided by the few foods and most vitamin supplements
- Vitamin D2 (ergocalciferol) provided by some supplements and found in very small amounts in mushrooms.
Both forms are metabolised in the same way, but the 25 hydroxyvitamin D3 has a longer half-life than 25 hydroxyvitamin D2. Hence supplements of vitamin D3 are considered more beneficial than supplements of vitamin D2.
The Healthy Start supplements
English CCGs and local authorities and Scottish health boards are required to provide them free of charge to the beneficiaries of the Healthy Start scheme and sell them at a fixed price to other clients. Unfortunately, availability of these supplements varies and in some areas they are only available in some NHS clinics but are not for sale to non-beneficiaries of the Healthy Start scheme. GP surgeries could stock and distribute or sell them to patients. The supplements can be ordered from NHS supply chain. More information can be found on the Healthy Start website. The Chief Medical Officer is considering making them universally free to all pregnant and breastfeeding women and children under five.12
Over the counter supplements
Both tablet and liquid form are available in pharmacies and supermarkets. Patients should be advised to buy Vitamin D3 supplements from brands sold in pharmacies as these have reliable quality control standards, e.g. Baby D, Boots, Colief, HealthAid, Vitabiotics, Wellkid.
Most multi vitamin supplements for infants, children, adults and pregnant and breastfeeding women sold in the UK include vitamin D along with other vitamins, but the vitamin D content varies and may not meet the recommendation.
Excess vitamin D taken as supplements could have detrimental effects on health.
The European tolerable upper intake levels of vitamin D are:
- infants 0-12 months: 25ug (1000IU)/day
- children 1-10 years: 50ug (2000IU)/day
- older children and adults: 100ug/day (4000IU)/day.13
Treating diagnosed vitamin D deficiency
Prescription supplements of high doses for the treatment of diagnosed vitamin D deficiency are listed in the BNF and BNFC. Some NHS areas have treatment protocols to follow.
Judy More works freelance and is a member on the Colief Expert Panel.
- Scientific Advisory Committee on Nutrition (2015)
- Public Health England and Food Standards Agency (2014)
- Clemens TL, Henderson SL, Adams JS, Holick MF. Lancet 1982: 1(8263): 74-76
- Holick MF. J Investig Med. 2011;59(6):872-80
- Dror DK. Curr Opin Obstet Gynecol. 2011 Dec;23(6):422-6.
- Bodnar LM, Catov JM, Hyagriv NS, et al. J Clin Endocrinol Metab 2007;92:3517e22.
- Cancer Research UK (2010)
- National Institute for Health and Care Excellence (2016) Nice Guidance 34 Sunlight Exposure: Benefits and Risks https://www.nice.org.uk/guidance/ng34
- Department of Health (2012) Letter from Chief Medical Officer to Healthcare Professionals: Vitamin D: Advice for at risk groups
- Department of Health (1998) The Stationery Office, London.
- National Institute for Health and Care Excellence (2014) https://www.nice.org.uk/guidance/ph56
- National Institute for Health and Care Excellence (2015)
- EFSA (2012) EFSA Journal 2012;10(7):2813 [45 pp.]. doi:10.2903/j.efsa.2012.2813