Vitamin D has hit the headlines as the ultimate immune support against COVID-19. However, the headlines may be overpromising and confusing both consumers and health professionals.
The focus on vitamin D during lockdown is indeed justified and the government's updated advice recommends a daily supplement of 10mcg for all individuals. To bring clarity on this topic, the BNF's latest Nutrition Bulletin highlights the importance of vitamin D, why the government has recommended supplements over food sources and reviews the evidence for the various health outcomes associated with this vitamin.
Why vitamin D supplements?
In April, the government updated it's current recommendations on vitamin D, stipulating that during lockdown, all individuals should be consuming a daily supplement of 10mcg. The reason behind it is simple; minimising exposure to sunlight during April through to September in the UK, means that we are avoiding our main source of vitamin D and are unlikely to maintain adequate status or stores to keep us going through the autumn and winter months.
Vitamin D food sources are scarce and not commonly consumed in the UK. Oil-rich fish and cod liver oil capsules are rich sources, whilst other animal foods provide some vitamin D e.g. egg yolks, offal and meat as well as fortified products such as a handful of breakfast cereals, the majority of non-organic plant-based drinks and alternatives to yogurt and some dairy. National Diet and Nutrition Surveys (NDNS) have consistently shown poor intakes even for those taking supplements.
Vitamin D deficiency is high in the UK
Additional to poor intakes, the NDNS and other independent UK studies have demonstrated significant vitamin D defiency in specific populations and an increase prevalence of rickets. Deficiency is classified as serum 25-hydroxyvitamin D [25(OH)D] concentrations below 25nmol/L:
- 39% teenage girls and 15% teenage boys - this is highly significant as bone mineral density is optimised during teenage years
- 19% men and 16% women aged 19-64 years
- 53% South Asian women
Thus the government adapted its recommendations back in 2016 to set a 10mcg daily recommended intake across all age groups. Additionally, for all children under 5 and all at risk groups unlikely to have adequate exposure to sunlight or have dark skin, the government recommended a daily all-year vitamin D supplement of 10mcg. For all other individuals, the government recommends a vitamin D supplement during the winter months to compensate for lack of dermal vitamin D production.
With lockdown currently imposed on all individuals, it is unlikely that anyone will have adequate sunlight exposure and thus we are all 'at risk' of vitamin D deficiency. It is therefore, not surprising that vitamin D supplements are now recommended to all during the summer months.
Can vitamin D help with our fight against COVID-19?
Early research indicates that vitamin D does have a role to play in our immune system and vitamin D receptors are present on beta and T-lymphocytes, macrophages and dendritic cells. However, there is a clear lack of randomised controlled trials to come to any definite conclusions. The complexity of the immune system and involvement of numerous other nutrients, does indicate that although an important component of the immune response, one nutrient alone is unlikely to be the solution.
Of more importance is the undisputed correlation between vitamin D status and bone health.
One daily 10mcg vitamin D supplement should be taken by all.
With a wealth of evidence demonstrating poor compliance with daily supplement intakes, the article goes on to discuss fortification of commonly consumed foods as a more effective national policy to ensure adequate vitamin D status for all.
Alpro providing vitamin D across all its range
Alpro drinks and alternatives to yogurts are fortified with vitamin D at 0.75mcg per 100ml/g as well as calcium and vitamin B12.