Approximately one-in-five adults and one-in-six children have inadequate vitamin D levels – but how much do you know about the different ways in which this deficiency can impede your patient’s life? WPR delves into the nutrient’s hidden depths.

Bolstering spirits, boosting activity, and brimming with opportunity, summer’s arrival in the UK sparks mass anticipation. However, many individuals fail to recognise the benefits which the brighter days lend to our wellbeing as well as our social life – particularly through the role of vitamin D and the nutrient’s crucial maintenance of calcium levels in the body; safeguarding the health of bones, teeth and muscles.

Produced by the body in response to sunlight, in the UK we attain most of our vitamin D from sunlight exposure from around late March / early April to the end of September. In the UK, sunlight doesn’t contain enough UVB radiation in winter (October to early March) for our skin to be able to make vitamin D. During these months – and often outside of them – we are heavily dependent on receiving vitamin D from food sources (including fortified foods) and supplements.

Vitamin D and Bone Health

Homing in on the role of vitamin D in the prevention of weakening bones, the National Osteoporosis Guideline Group (NOGG) 2017: Clinical Guideline for the Prevention and Treatment of Osteoporosis outlines, ‘In postmenopausal women and older men receiving bone protective therapy for osteoporosis, calcium supplementation should be given if the dietary intake is below 700 mg/day, and vitamin D supplementation considered in those at risk of, or with evidence of, vitamin D insufficiency’.

However, it must be remembered that where rapid correction of vitamin D deficiency is required, such as in patients with symptomatic disease or those about to commence treatment with a potent antiresorptive agent, the recommended treatment regimen is based on fixed loading doses followed by regular maintenance therapy. The Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management subsequently advises that calcium / vitamin D combinations should ‘not be used as sources of vitamin D’ for fixed loading regimens due to the ‘resulting high dosing of calcium’.

Vitamin D and the Immune System

Fresh insights have been directing our attention to the significance of vitamin D through its association with our immune system, and how its deficiency may influence susceptibility to autoimmune diseases.

Shedding light, a University of Edinburgh team focussed their research on how vitamin D affects a mechanism in the body’s immune system – dendritic cells’ ability to activate T cells. In healthy people, T cells play a crucial role in helping to fight infections; in people with autoimmune diseases, however, they can start to attack the body’s own tissues.

By studying cells from mice and people, the researchers discovered that vitamin D caused dendritic cells to produce more of a molecule called CD31 on their surface and that this hindered the activation of T cells. They subsequently observed how CD31 prevented the two cell types from making a stable contact – an essential part of the activation process – and the resulting immune reaction was far reduced.

Vitamin D and Mental Health

Although prominently linked to bone health – and, at recent, various non-bone health outcomes, such as inflammation and diabetes – the potential relationship between vitamin D and mental health has been shrouded in uncertainty. Addressing this gap in knowledge a study by researchers from The Irish Longitudinal Study on Ageing at Trinity College Dublin got underway – demonstrating for the first time in Ireland that a deficiency in vitamin D was associated with a substantial increased risk of depression over a four-year follow-up period.

This finding remained robust after controlling for a wide range of relevant factors, including depressive symptoms, chronic disease burden, physical activity and cardiovascular disease. Furthermore, excluding participants taking anti-depressant medication and vitamin D supplementation from the analyses did not alter the outcome.

But what is the science behind the correlation between insufficient vitamin D and depression? The authors have suggested that the findings could be due to the possible direct effect of vitamin D on the brain in that given the structural and functional brain changes seen in late life depression, vitamin D may have a protective effect in attenuating these changes.

Vitamin D and Children

The risk of fractures in those with inadequate vitamin D has long been an area of interest for clinicians – with a report last year weighing in and showcasing the important link between low vitamin D levels and the severity of fractures in children caused by low-energy, less traumatic events, such as falling off a bike or falling while running.

The data indeed revealed that children who are vitamin D deficient have a greater risk of having more severe forearm fractures requiring surgical treatment and suggested how we can intervene to help.

‘This study provides an important takeaway for parents and paediatricians,’ explained Dr Pooya Hosseinzadeh, MD, Assistant Professor, Department of Orthopaedic Surgery at Washington University School of Medicine in St Louis.

‘If a child does have a forearm fracture, we would encourage the physician to check the patient’s vitamin D levels. The good news is that in most cases, children can reduce deficiency with a vitamin D supplement and increasing outdoor activity.’