Vitamin D – the essential vitamin

International studies have explored the role of vitamin D with its link to improved health outcomes. There is an increasing awareness of the possibility of this nutrient to have an impact on worldwide health, potentially altering the management of both chronic and acute health conditions. The initial discovery of this expansive vitamin began in 1913. Over 100 years later, there are over 80,000 journal articles discussing the potential effectiveness of this vitamin within the clinical domain.

Sources of Vitamin D

For most people, solar UVB radiation (wavelengths 280-315 nm) is the main natural source of vitamin D3 (cholecalciferol). Sunscreens and high skin pigmentation can reduce the UVB-mediated production of D3 – for example, SPF15 factor sunscreen can reduce D3 production by 99% (Passeron et al., 2019).

Whilst dietary sources of vitamin D are limited, animal products such as oily fish and egg yolks are the highest dietary source (Holick et al., 2006). The vitamin D found in oily fish is expected to derive from an accumulation in the food chain originating from microalgae. Certain algae and lichen species now provide a natural source of D3 for those who follow a plant-based diet. Vitamin D2 is used for food fortification and has a lower affinity to vitamin D receptor sites, thus requiring daily intake. Evidence demonstrates that vitamin D2 does not increase blood levels of 25-hydroxyvitamin D3(25(OH)D) to the same intensity compared with vitamin D3 (Henríquez and Jesús Gómez de Tejada Romero, 2020).

Values: How much and where?

In the global community, vitamin D deficiency and insufficiency is seen as a major public health problem in all age groups, even in countries with a high daily sun exposure (Chakhtoura et al., 2018). In addition, some researchers have suggested that a low vitamin D intake combined with increasing obesity rates are increasing the rates of chronic disease (Palacios and Gonzalez, 2014; Carrelli et al., 2017; Umemura et al., 2014).

Contrary to common belief, countries with long winters have lower deficiency rates compared to sunnier locations (Chakhtoura et al., 2018; Palacios and Gonzalez, 2014; Mogire et al., 2020). This suggests both the use of supplementation and the fortification of common food items (Guo et al., 2019).

A prolonged debate of the minimum level of vitamin D status is of international concern (Palacios and Gonzalez, 2014). Various international institutions state levels below 50 nmol/L (<20 ng/mL) are unacceptable (Drincic et al., 2012; Vanlint, 2013). In addition, clinical trials and studies have demonstrated improvements in health outcomes when levels of vitamin D are above 75 nmol/l (30 ng/ml) (Chun et al., 2019; Spiro and Buttriss, 2014).

Vitamin D and Magnesium

Magnesium plays a crucial role in the activation of vitamin D, working with the hydroxylase family of enzymes present in the kidney and liver. Evidence has demonstrated that suboptimal levels of magnesium can hinder this conversion (Rosanoff et al., 2016). The process by which vitamin D3 is transported in the blood between the skin, liver, and kidney to numerous target tissues utilises magnesium, whilst it is also required for the activity of the Vitamin D Binding Protein (Deng et al., 2013). Several studies have demonstrated that magnesium supplementation significantly reversed resistance to vitamin D treatment in patients with rickets (Deng et al., 2013).

The status of magnesium can be affected by many lifestyle factors and reduced dietary intake. In the UK, the last dietary food survey highlighted that a high portion of the population did not meet the RNI (Mann et al., 2015). Thus, this may be the contributing factor to the low vitamin D status within various population groups.

Absorption

Vitamin D is a fat-soluble vitamin, meaning that it does not dissolve in water and is absorbed best in your bloodstream when paired with high- fat foods. Supplements suspended in sunflower seed oil aid absorption.

Assessing Vitamin D Status

Vitamin D is best assessed via measuring serum 25(OH) D3 levels (Paxton et al., 2013). Serum 25(OH)D levels can be used to determine if there is a deficiency and the optimal level of supplementation.

The level of vitamin D3 which indicates deficiency and excess varies between sources. A general indication of optimal serum concentrations of 25(OH)D is between 75 and 135 nmol/L (Bischoff-Ferrari et al., 2006; Alshahrani and Aljohani, 2013). However, up to 250 nmol/L may be considered normal in situations of high sun exposure.

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