What is the scale of the problem in the UK?

Hypovitaminosis D affects adults in epidemic proportions in Western societies⁽Reference Calvo, Whiting and Barton^2, Reference Prentice³⁾, which is a problem aggravated by Western lifestyles with long hours of indoor work and by avoidance of sunshine aimed at reduction in skin cancer risks (Table 1). Vitamin D deficiency ( < 25 nmol/l) is more common in women than in men (for example, 9·2 v. 6·6 %, respectively, in British 45-year-olds)⁽Reference Hyppönen and Power⁴⁾, and pregnancy is known to represent a particularly high-risk situation. However, as we will discuss in the following section, in the UK, there is currently no consensus on advice on vitamin D supplementation to pregnant women or generally agreed guidelines for relevant health care providers. Lack of consistent guidance leads to mixed messages, which make it difficult to effectively implement strategies for the primary prevention of vitamin D deficiency.

Table 1 Barriers to adequate vitamin D intake and sunlight-induced skin synthesis in pregnancy

SACN, Scientific Advisory Committee on Nutrition.

The return of rickets in the UK

There is a long history of population-based approaches for the prevention of vitamin D deficiency in Britain⁽Reference Bivins⁵⁾. By the mid-19th century, it was appreciated that rickets was prevented and cured by summer sunshine or by taking cod liver oil⁽Reference Rajakumar⁶⁾. The discovery of vitamin D in the 1920s led to regular outdoor ‘airing’ of infants and routine cod liver oil consumption by many mothers and children⁽Reference Bivins^5, Reference Rajakumar⁶⁾. Indeed, neonatal/infantile hypocalcaemia and rickets had virtually disappeared by the 1930s. As a result of this knowledge, ergocalciferol was added to National Dried Milk during World War II, and cod liver oil was included as one of the five welfare foods distributed by the Ministry of Food to expectant/nursing mothers and young children⁽Reference Berry⁷⁾. Since World War II, vitamin D supplementation has been consistently recommended during pregnancy⁽Reference Bivins^{5, 8,} Reference Shaw and David⁹⁾. However, after the war, uncontrolled vitamin D fortification of baby milks and baby foods provided intakes of up to 100 μg/d (4000 IU/d), which caused many cases of infantile hypercalcaemia⁽Reference Bivins^5, Reference Arneil^10, Reference Berry¹¹⁾. Uncontrolled vitamin D fortification was then banned⁽Reference Berry¹¹⁾, followed by resurgence of rickets in immigrant communities during the 1960s⁽Reference Bivins^5, Reference Arneil^12, Reference Stewart, Mitchell and Morgan¹³⁾. Cod liver oil remained available at antenatal clinics, but uptake was poor in immigrant populations⁽Reference Datta, Alfaham and Davies¹⁴⁾. Routine offers of cod liver oil (rich in vitamin A) to pregnant mothers ceased in the 1990s following formal advice from the Chief Medical Officer when the teratogenicity of excessive vitamin A intake was appreciated⁽¹⁵⁾. No provision was made for continued vitamin D supplementation of pregnant mothers. This left women dependent on the combination of a national diet known to be poor in vitamin D and sun-induced skin synthesis that is effective in increasing serum 25-hydroxyvitamin D (25(OH)D) concentrations only for 5–6 months of the year⁽Reference Hyppönen and Power^{4, 8)}. The benefits of modest supplementation of immigrant mothers had been demonstrated in the UK by the 1990s⁽Reference Bivins^5, Reference Arora and Arora¹⁶⁾, suggesting that the resurgence of rickets was predictable and largely preventable had routine vitamin D supplementation been continued⁽Reference Bivins⁵⁾.

Current conflicts in advice

The UK Department of Health (DoH) re-enforced their advice⁽¹⁷⁾ for pregnant and breast-feeding mothers to ensure that they achieved intakes of vitamin D (10 μg/d (400 IU/d)) in 2007. This followed recommendations of the Scientific Advisory Committee on Nutrition⁽⁸⁾ (Table 2) and a resurgence of rickets, especially in immigrant communities with high prevalence of vitamin D deficiency⁽Reference Prentice^3, Reference Wharton and Bishop^18–Reference Odeka and Tan²¹⁾. DoH advice effectively endorses supplementation as diet provides little vitamin D, and sunlight-induced synthesis is limited in Britain⁽Reference Hyppönen and Power^{4, 8)}.

Table 2 UK sources of current advice on vitamin D supplementation in pregnancy and conflicts on who should be supplemented

*  All links are as accessed on 9 July 2009.

The recent DoH re-enforcement of vitamin D supplementation in pregnancy coincided with a conflict in advice being developed by the National Institute for Health and Clinical Excellence on Antenatal Care (‘healthy pregnant mothers should not be routinely supplemented with vitamin D’, September 2007) and on Maternal and Child Nutrition (endorsing existing DoH guidelines, July 2007). The final recommendation was made by the National Institute of Health and Clinical Excellence Guideline Review Panel, and, in contrast to current DoH guidance, it did not endorse vitamin D supplementation for all pregnant women. Instead, it stated that ‘all women should be informed… about the importance for their own and their baby's health of maintaining adequate vitamin D stores during pregnancy and whilst breastfeeding’, and that ‘in order to achieve this, women may choose to take 400 IU/d as in the Healthy Start Multivitamin supplement’^{(22, 23)}. Continuing confusion in the UK recommendations is highlighted by the inclusion of vitamin D as one of the vitamins to be provided free of charge to low-income mothers as part of the Healthy Start Scheme (previously known as the Welfare Food Scheme), despite the relatively weak social differences in vitamin D status seen in the UK⁽Reference Hyppönen and Power⁴⁾ and the lack of systematic implementation of vitamin D supplementation recommendations for other pregnant mothers. There have also been severe problems in the distribution of Healthy Start vitamins, with manufacturing being stopped due to ‘lack of demand’⁽Reference McGee²⁴⁾. Currently, the UK is the only one of the thirty-one European countries with a recommended daily vitamin D intake of 0 for women of child-bearing age⁽Reference Doets, de Wit and Dhonukshe-Rutten²⁵⁾, and therefore, the UK is doing nothing to reduce the risk of women becoming vitamin D deficient before they become pregnant.

Conflicting advice on maternal vitamin D intake is not unique to the UK. The North American health authorities are debating, not about whether to supplement vitamin D, but only about the dosage of vitamin D that should be provided. The Canadian Paediatric Society recently recommended that ‘all pregnant mothers should take vitamin D 50 μg/d (2000 IU/d) throughout pregnancy’⁽²⁶⁾, while shortly afterwards, the Federal Department of Health Canada re-enforced its recommendation of 5 μg/d (200 IU/d) for pregnant and breast-feeding women, publicly discounting the recommendations of the Paediatric Society. Currently, the European Commission recommends 10 μg/d (400 IU/d) vitamin D during pregnancy⁽²⁷⁾, while the WHO recommendation is set at 5 μg/d (200 IU/d)⁽²⁸⁾.

Gaps in the evidence and differences in its interpretation

Inconsistency in advice given by health authorities can arise from differences in the interpretation of available evidence and in the perceived importance of vitamin D deficiency in pregnancy. Furthermore, opinions about the safety of dosages>10 μg/d (400 IU/d) in pregnancy differ⁽⁸⁾. As reviewed above, historical data suggest that the recommended dosage of 10 μg/d (400 IU/d) is safe and effective in preventing severe clinical vitamin D deficiency, rickets in children and osteomalacia in adults⁽Reference Bivins^5, Reference Shaw and David⁹⁾. However, the physiological effects of 1,25-dihydroxyvitamin D (the active hormonal metabolite) are known to extend beyond Ca metabolism and bone health, and evidence is accumulating to suggest that vitamin D intakes required to achieve optimal benefits are likely to be much higher⁽Reference Hollis and Wagner^29, Reference Holick³⁰⁾.

The public health problem, what is being done and what more should be done

As stated in the Scientific Advisory Committee on Nutrition Update on Vitamin D⁽⁸⁾, there is concern that vitamin D ‘recommendations are overlooked by health professionals, as well as by the general public’, and further that the ‘uptake of vitamin drops in the UK is very low even amongst those entitled to receive free supplies’. The recent provision of supplements containing 10 μg (400 IU) of vitamin D to pregnant/breast-feeding women and their offspring should lead to improvements in the situation, provided that the supply chain problems can be overcome⁽Reference McGee²⁴⁾.

British immigrants are recognised as at ‘high risk’ of hypovitaminosis D, but the problem is also common in pregnant White women, even when living in the Southern England⁽Reference Javaid, Crozier and Harvey⁴⁷⁾. As can be seen in Fig. 1, 90 % of white pregnant mothers in the Avon Longitudinal Study of Parents and Children⁽Reference Golding, Pembrey and Jones⁵⁹⁾ had 25(OH)D concentrations < 50 nmol/l during winter and spring; 28 % were seriously deficient ( < 25 nmol/l), and virtually no one reached 75 nmol/l (currently considered optimal). Over the year, 60 % of expectant mothers (approximately 403 000 English/Welsh women) are likely to require vitamin D supplementation for avoidance of serum 25(OH)D < 50 nmol/l (90 % being White). Over 150 000 mothers will have deficiency ( < 25 nmol/l), and 59 % of these being White (estimated from data presented in Fig. 1 and published prevalence rates for non-White British immigrants⁽Reference Yu, Sykes and Sethi⁵⁷⁾). As seen in Fig. 1, hypovitaminosis D in White women in the UK is largely a problem during winter and spring, suggesting that treatment during these seasons would benefit most women.

Fig. 1 Prevalence of hypovitaminosis D in pregnant White women living in Southern England (Avon Longitudinal Study of Parents and Children study⁽Reference Golding, Pembrey and Jones⁵⁹⁾, pilot sample, n 354). Error bars represent 95 % CI for prevalence. ■, < 25 nmol/l; , < 50 nmol/l; , < 75 nmol/l.

The UK Health Minister emphasised (December 2007) that ‘women should contact their GP for a blood test if they think they may be lacking the vitamin’ (Table 2). However, this approach does not allow for the high prevalence of hypovitaminosis D, for the high cost of serum 25(OH)D assays (currently approximately £10·50–£25 depending on the assay and laboratory) or for the undesirability of delays in starting supplementation while awaiting results. Indeed, given the data that have been discussed already, it can be argued that relatively little is gained by measuring individual 25(OH)D concentrations since routine supplementation of a pregnant/breast-feeding woman at 10 μg/d (400 IU/d) can currently be provided for £3·64/year⁽Reference McGee²⁴⁾.