At least 2 billion people worldwide are currently affected by micro-nutrient deficiencies and despite the UK being a developed country with high food availability, some British children still suffer deficiencies. During pregnancy and childhood where physiological growth occurs at a rapid rate, its well known an intake of Vitamin D is required in sufficient amounts during these crucial periods of growth. Mothers with low 25-OHD serum levels who fail to intake or supplement the recommended amounts of vitamin D during pregnancy and who breastfeed past 6 months without supplementation are the biggest causes of childhood vitamin D deficiency. Other factors that affect vitamin D status in children is inadequate UVB exposure and/or low intake of dietary sources include fortified foods or supplements. Vitamin D deficiencies seems to be a problem of our awareness about the importance of nutrition and of the availability of supplementation or food sources that could be improved with fortification rather than a problem of race and age.
Micro-nutrients are organic and inorganic substances composed of vitamins and minerals that we need from our diet which are necessary for cellular function, physical growth and tissue repair during all stages of life (Merson, Black and Mills, 2012). At least 2 billion people worldwide are currently affected by micro-nutrient deficiencies (Unitedcalltoaction.org, 2016) and despite the UK being a developed country with high food availability, some British children still suffer deficiencies. Currently many children and adolescents across the whole of Europe including Britain have all shown the same consistent deficiencies of at least six micro-nutrients (Kaganov et al., 2015).
Micro-nutrient deficiencies can affect all age groups but children are a particularly vulnerable group, especially those from low income families (Casey et al., 2001). The social and economic costs of micro nutrient deficiencies in women and children are also thought to be significant (Darnton-Hill et al., 2005). During pregnancy and childhood where physiological growth occurs at a rapid rate, it is well known an intake of micro-nutrients are required in sufficient amounts during these crucial periods of growth. Adverse effects from nutrient deficiencies are well documented (Viteri and Gonzalez, 2002) (SCN.,2004) and the effects of a prolonged deficiency is catastrophic.
One micro-nutrient deficiency that has made a come back since the industrial revolution is vitamin D. Deficiencies in vitamin D results in serious physical growth deformities (Abrams., 2002). Vitamin D deficiencies (VDD’s) are now being frequently observed children as a result of poor intake, inadequate sunlight exposure or because of a deficiency in the mother during pregnancy or breastfeeding. The long term outcomes from these deficiencies can lead to limitations in the quality of a childs future. So the importance of an adequate intake of vitamin D during pregnancy and childhood cannot be overstated, although requirements are often not being met. Therefore the focus of this review will be based on the prevalence and causes of vitamin D deficiency during pregnancy and among British children. This review will derive from recent research mainly within the last 15 years.
Vitamin D intake and recommendations
Two main forms of vitamin D exist as vitamin D2 (ergocalciferol) which can be attained predominantly from animal foods and vitamin D3 (cholecalciferol) which is photochemically synthesised cutaneously in human and animal skin. Vitamin D converts into one of its active forms 25-hydroxyvitamin D (25-OHD) of which serum levels can be measured and is the main clinical method used for assessing vitamin D status. Clinical deficiency is classed as a 25-OHD serum level of <25 nmol/L and a vitamin D insufficiency <50nmol/L, both inadequate levels for good health (Thurston et al., 2015). VDD (vitamin D deficiency) is now proving to be associated with many health problems (Macneil, 2008) (Gominak and Stumpf, 2012) (Zoler, 2012) (Reid, 2015) but is more widely known for effects on bone metabolism. This is important particularly for children and adolescents as 90% of bone density is laid during the first two decades of life (Eufic.org, 2014).
Vitamin D measurements and recommendations of intake can be confusing too as food labels and recommendations often use both µg and IU of units of measurements, which both have different equivalences. To avoid confusion it’s important to remember that every 1µg of vitamin D is equivalent to 40IU of vitamin D. Recommendations on vitamin D intake was set out by the Committee on Medical Aspects of Food and Nutrition Policy (COMA) in 1991. It was based on the assumption that the population would receive sufficient vitamin D intake in the summer resulting in sufficient stores for winter. Therefore, reference nutrient intakes (RNI’s) were only issued for vulnerable groups such as Infants and children aged under 4 years, who were advised an intake of 7-8.5µg/day (280-340IU/day), and pregnant women and breastfeeding women, advised an intake 10 μg/day (400 IU/day) via supplementation (Panel on Dietary Reference values of the Committee on Medical Aspects of Food Policy., 1991). However, these dietary values are not being met by these groups today and may also not be in line with the lifestyle and cultures of today’s population who spend more time indoors or out of sunlight exposure and inactive than is recommended (Matsuoka et al., 1993) (Certain and Kahn, 2002).
Young women in the UK, from mixed ethnic backgrounds, also only average a daily intake of only 3μg of vitamin D and less than 1% of young women consume more than the RNI of 10μg/day (Marriott and Buttriss, 2003). This is worrying considering 10μg/day is the recommended intake advised during pregnancy and breastfeeding to prevent deficiency which can lead to growth impairments or osteoporotic bone injuries later on in life. Mothers with low 25-OHD serum levels who fail to intake or supplement the recommended amounts of vitamin D during pregnancy and who breastfeed past 6 months without supplementation are the biggest causes of childhood VDD (Thomas et al., 2011) (Aljebory, 2013). Nutritional rickets is regarded as a disease of VDD which results in serious bone deformity and the prevalence of rickets, is currently at its highest since 1963 (Goldacre, Hall and Yeates, 2014).
Vitamin D deficiency in cultural and ethnic groups
Culture and ethnicity are other factors that exacerbate childhood VDD prevalence in the UK, especially when dietary intake of vitamin D is already low and British weather is notoriously unreliable as a sustainable source of sunlight (UVB) exposure. Six Infants aged 10-28 months born in the UK of mothers that failed to supplement vitamin D during pregnancy and during breastfeeding were referred to a paediatric clinic. All infants presented with low serum 25-OHD levels and were subsequently diagnosed with florid rickets as a result of VDD. Some of the mothers were postgraduate students and some were immigrants but most of the mothers were traditional Muslims who concealed their skin in public for religious reasons (Mughal et al., 1999).
Since VDD is particularly prevalent among sunlight deprived individuals, such as women practising religions that require skin concealment, the current dietary recommendations may be inadequate for these individuals to attain sufficient 25-OHD levels who receive little to no UVB exposure (Glerup et al., 2000). Results from a UK study on 78 women aged 18-36 of South Asian origin showed 94% of these women to have VDD evident by low serum 25-OHD levels (Dobson, 2007). Further research supports the UK recommendations of UVB exposure in the summer to be inadequate for adults of South Asian ethnicity (Farrar et al., 2011) which means compensations must be made through dietary intake. Repeated research has also shown children of ethnic minority groups tend to be at a higher risk of vitamin D deficiency than caucasians (Shaw, 2002) (Brenner and Hearing., 2007) with high prevalence of VDD among Somali children (Modgil et al., 2010) and asian children (Zlotkin and Blumsohn, 1999). This obviously raises concerns for children born in the UK of mothers who are of a particular religion or ethnicity and of Mothers who are likely to have VDD before, during and after pregnancy while breastfeeding, unless of course specific dietary needs are met.
Vitamin D deficiency in Caucasians and general population
Many Caucasian women and children of the population however despite differing levels of ethnic susceptibility to VDD are still vitamin D deficient and studies have even shown even those in sunlight rich countries are susceptible to VDD (Bettica et al., 1999) (Gannagé-Yared et al., 2000) .
A study involving 1414 Caucasian women has shown females in the UK with fair skin have lower serum 25-OHD levels than Caucasian females with dark skin (Glass et al., 2009). This outlines variability in responsiveness to UVB exposure which ultimately affects vitamin D status and since the effects of VDD on bone health in Caucasian and non-Caucasian women are the same (SA, 2011) the prevalence of VDD in Caucasian women should not be overlooked either.
A longitudinal study involving 99 British Caucasian women who were pregnant showed 44% of the women were vitamin D deficient (25-OHD <25nmol/L) at 20 weeks gestation and 96% of women were vitamin D insufficient (25-OHD <50nmol/L) at 12 and 20 weeks . All women seemed to have improved vitamin D status by 35 weeks compared to 12 weeks gestation, but even then 16% were still vitamin D deficient and 75% still had insufficient levels. Some women also took vitamin D supplements which led to higher serum 25-OHD levels than those who didn’t, but vitamin D insufficiency was still present even with supplementation (Holmes et al., 2010).
A study conducted on children born of vitamin D deficient mothers showed all children were born deficient in vitamin D. However, vitamin D status in the infants quickly normalised after receiving an intake of 10μg/day (400 IU/day) at 2 weeks of age (Bergström, Blanck and Sävendahl, 2013) which intake is the RNI recommended for pregnant and breastfeeding women. Research shows that when baseline serum levels from groups were < 75 nmol/L, for every 1μg of vitamin D supplemented 25-OHD levels are raised by 2 nmol/L. However, when groups were clinically deficient (<25nnmol/l 25-OHD) or insufficient (<50nnmol/l 25-OHD) in vitamin D, there was significant value in providing an additional 10μg per day of vitamin D.
In a longitudinal UK study nearly a third of women studied had insufficient maternal 25-OHD levels (<50nmol/L) and 18% had maternal levels of 25-OHD levels indicative of deficiency (<25nnmol/L). These low 25-OHD levels during pregnancy resulted in reduced bone mass in their children at the age of 9 (Javaid et al., 2006). A cohort study showed the same results of reduced bone density observed in their offspring at 20 years of age born of mothers who were vitamin D deficient during pregnancy (Zhu et al., 2014). This highlights the need for national preventative and educational strategies aimed at the entire population with particular focus towards UK women of child bearing age.
Given the current rise in VDD It seems logical to make vitamin D supplements available to pregnant women through their GP in the same way folic acid is, although it was concluded by The National Institute for Health and Care Excellence in 2003 that vitamin D should not be routinely administered to all pregnant women (NICE, 2003). Since then though clear relationships between maternal 25-OHD status and offspring health have been made apparent (Sabet, 2012) (Young et al., 2012) (Rebecca et al., 2013). Research has shown doses of 50μg/day of vitamin D supplementation taken by mothers during pregnancy and during breastfeeding has shown to protect infants from being born into deficiency and up until 8 weeks of age (March et al., 2015). Firm recommendations on vitamin D supplementation intakes as high as the maximum upper tolerable level (UL) to prevent deficiency has also been suggested (Holick et al., 2011). However others state the evidence is still insufficient to support definitive clinical recommendations of vitamin D supplementation during pregnancy (Harvey et al., 2014) even though supplementation does raise serum 25-OHD levels to recommended amounts, larger randomised controlled trials have been prompted (Pérez-López et al., 2015).
Vitamin D status among children
Apart from mothers with low maternal vitamin D status during pregnancy and breastfeeding and ethnic susceptibility, other factors that affect vitamin D status in children are inadequate UVB exposure and/or low intake of dietary sources including fortified foods or supplements (Hartman, 2000). Excessive sunscreen use has been recognised as a factor in causing VDD in Caucasian children (Galibois, Rhainds and Gagné, 2001) which unfortunately mimics the same problem ethnic groups face who have low UVB absorption rates due to dark skin pigmentation and its use on children has been put into question (Norval and Wulf, 2009). This makes dietary intake or supplementation of vitamin D seem like the only plausible option for achieving ample vitamin D status. Although intakes of dietary sources among children are poor especially in countries where optional or no mandatory fortification policy is in place (Prentice, 2008). The diets of 755 children aged 18 months-3.5 years from the Avon Longitudinal Study of Parents and Children (ALSPC) in the UK were analysed. It was found that all of the childrens diets were low in dietary sources of vitamin D and were all below the recommended intake for vitamin D. It also found that milk was the main source of what little vitamin D they did consume and it was suggested that an increase in fortification levels of vitamin D would most likely help children receive adequate intakes (Cribb et al., 2014). In a study involving 252 Irish children and adolescents, more than half had 25-OHD serum levels at <50nmol/L which is considered insufficient (Carroll et al., 2014). Educational methods and health promotion have proven effective at increasing intakes of dietary sources of calcium and vitamin D among children (Spence et al., 2013) (Pampaloni et al., 2015) and may work in concert with a similar educational programme aimed at parents that could reinforce what’s being taught in children.
Children pay the price because of their Mothers inadequate nutritional intakes during pregnancy and breastfeeding and largely because of their Mother’s lack of awareness about the importance of vitamin D. Awareness and education early on in pregnancy may lay the foundations for a vitamin D sufficient future for future generations in the hope that the message of vitamin D importance is passed on to prevent an issue of the past and present becoming an issue of the future. An improved national fortification policy aimed at frequently consumed foods may help resolve vitamin D deficiency, as will national supplementation recommendations on vitamin D during pregnancy and breastfeeding which has shown to improve vitamin D status. Research is showing vitamin D deficiencies and rickets to be on the rise and vitamin D deficiency is clearly being observed in pregnant and breastfeeding women and in children of all ages and ethnicities. Vitamin D deficiencies seems to be a problem of our awareness about the importance of nutrition and of the availability of supplementation or food sources that may be improved with fortification rather than a problem of race and age.
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