Vitamin D continues to confuse patients and clinicians alike. There are a number of contributory factors, including mixed messages from the media, the health food industry, clinicians and public health experts.
In practice, the role of vitamin D in bone health remains a topic of debate with even more confusion over vitamin D in non-skeletal disorders such as auto-immune disease, neurodegenerative disease, cancer, mental health and cardiovascular disease.
We see the provision of vitamin D testing increasing, both in the NHS and by private providers, and an increase in the number of vitamin D preparations, both prescribed and purchased over-the-counter. However, NHS England recently suggested that much prescribing of vitamins and minerals is of 'limited clinical effectiveness'.
In 2013, the National Osteoporosis Society (NOS) produced clinical guidelines, based on available evidence at the time, which have proved valuable to healthcare professionals and patients alike. However, since then, NICE public health guidelines (PH56) have been published, and the Scientific Advisory Committee on Nutrition (SACN) has reported on vitamin D.
The NOS guideline has therefore been revised, focusing again on musculoskeletal health, since evidence for interventions elsewhere is far from clear. It aims to answer clinical questions relevant to busy clinicians, which are explained below.
Who should we test and treat for vitamin D deficiency?
It is important to consider vitamin D deficiency in the differential diagnosis for patients with musculoskeletal symptoms, such as bone pain or muscle weakness.
Plasma 25(OH) vitamin D (25(OH)D) level, measured by an accredited laboratory, is the best estimate of vitamin D status. However, for most patients with osteoporosis, and those who sustain a fragility fracture, vitamin D testing is not obligatory.
In light of the SACN report, the definition of vitamin D deficiency has been revised, although it is still based on plasma 25(OH)D:
- Less than 25 nmol/L is deficiency and treatment is recommended
- Between 25–50 nmol/L may represent an inadequate vitamin D status and treatment is recommended if the patient has:
- a fragility fracture
- diagnosed osteoporosis
- high fracture risk
- antiresorptive medication
- symptoms suggestive of vitamin D deficiency
- reduced sunlight exposure due to religious/cultural dress code, dark skin, etc.
- a raised PTH
- treatment with antiepileptic drugs or oral glucocorticoids
- Greater than 50 nmol/L is sufficient.
How should we treat with vitamin D?
Oral vitamin D3, also called colecalciferol, is the treatment of choice for vitamin D deficiency.
Ergocalciferol (vitamin D2), which is of plant origin, is not recommended for treatment unless patients are unable to take vitamin D3, for example where they have concerns about the animal source of vitamin D3. The NHS Specialist Pharmacy Service has published a helpful list of preparations of vitamins D3 and D2, which shows which preparations are suitable for those on a vegetarian or vegan diet.
A fixed-loading phase over a few weeks, with a total dose of up to 300,000 IU of vitamin D, is recommended for the treatment of symptomatic vitamin D deficiency, or the correction of inadequate vitamin D status, before treatment with potent antiresorptive drugs and this should be followed by maintenance therapy of 20 µg (800 IU) or more daily.
If co-prescribing vitamin D with an oral bisphosphonate, loading is not required and a maintenance dose will usually suffice. This may be given as a daily, weekly or monthly regimen. Routine co-prescription of calcium with vitamin D is unnecessary, as dietary calcium intake is satisfactory for the majority of people. If unsure, a dietary calcium calculator such as the one hosted at the University of Edinburgh may help in decision making.
How should we monitor patients?
A month after the initiation of treatment with vitamin D, serum adjusted calcium should be measured. Serial estimates of 25(OH)D are seldom required but may be helpful for patients who remain symptomatic from presumed vitamin D deficiency or have difficulties with malabsorption or adherence to therapy.
Can we give too much vitamin D?
Vitamin D toxicity is highly unlikely if the NOS treatment regimens are followed, as the agreed safe upper limit for long-term intake of vitamin D is 4,000 IU (100μg) per day. Hypercalcaemia is a risk in patients with disorders of calcium homeostasis, such as primary hyperparathyroidism or granulomatous disease, which may be occult, so checking serum adjusted calcium as already outlined is a sensible precaution.
There is also evidence that high dose vitamin D may paradoxically increase the risk of falls, particularly in older people and those prone to falling.
- Dr Aspray is a consultant physician and director of the bone clinic at Freeman Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust and honorary clinical senior lecturer at Newcastle University
The full National Osteoporosis Society guideline is available here, which includes more detail with sources for the evidence used.