How Should GPs Assess Vitamin D Deficiency?

New National vitamin D guidelines from the National Osteoporosis Society

(New guidelines on vitamin D supplementation have been published by the National Osteoporosis Society. These have been endorsed by the Royal College of Nursing, Bone Research Society, British Dietetic Association, Paget's Association., International Osteoporosis Foundation, UK Clinical Pharmacology Association, Primary Care Rheumatology Society, Royal Pharmaceutical Society, British Orthopaedic Association, Society for Endocrinology)

Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management

These guidelines do not address supplementation in pregnant women, although this is covered in NICE guidance.

The importance of vitamin D guidelines

Guidelines to ensure adequate vitamin D levels are important because in the UK we become vitamin D deficient every year between October and April. Many high-risk frail people are also housebound throughout the year. People who have had a previous skin cancer will have been advised not to sunbathe, and others may be on medications (such as amiodarone) that are a contra-indication to sunbathing.

Rickets, a disease associated with Victorian times, is now returning so efforts to combat the condition are needed. Furthermore, vitamin D repletion is important to ensure efficacy of bone-strengthening treatments in our aging population, as is calcium repletion.

Most elderly patients have dietary deficiency of calcium either because they are trying to cut down their cholesterol, or are too poor on a pension to eat properly. The housebound /residential care home patients rarely get out, even when the sun occasionally shines. For drugs like Denosumab and zoledronate it is often part of agreed protocols that the vitamin D level has to be >50 nmol/L to give the drug. Simply by correcting vitamin D deficiency you can make people feel better, sometimes relieve myalgia (especially in patients on aromatase inhibitors), and improve muscle strength reducing risk of falls and fracture, as well as ensuring the efficacy of the active treatment.

The British National Formulary (BNF) now lists a variety of vitamin D formulations: alone or in combination with calcium. Most people don't like taking calcium + vitamin D tablets because they are too gritty, 'taste like chalk', 'are too sweet', or give constipation and/or headaches. Some patients stopped taking calcium + vitamin D supplements after publication of Prof Ian Reid's Meta analysis. This showed that if you had enough calcium in your diet (>700 mg calcium/day) and you took calcium and vitamin D supplements, you had a 40% increased risk of heart attack and stroke (www.rheum.med.ed.ac.uk/calcium-calculator). There is still huge controversy about calcium supplementation versus dietary intake, which this guideline neatly sidesteps.

There are some new high-dose vitamin D (cholecalciferol or vitamin D3) listed in the BNF so that GPs can prescribe vitamin D3 alone on an FP10, to correct vitamin D deficiency (InVita D3 50,000 IU once a week for 6-8 weeks and re-check, or the 3,200 IU Fultium once daily for 6-8 weeks and recheck) or a maintenance dose (Fultium 800 IU once daily, or Invita D3 1400-2000 IU once a day): the advantage of this for our frail elderly population is the medication can go in the Nomad, so improving concordance, rather than an over the counter preparation which will be forgotten about.

It should be noted that Fultium contains peanut oil so is not suitable for people with peanut allergies. InVita D3 contains olive oil. It should also be noted that BOTH preparations are made from irradiation of lanolin from sheep's wool so may be unacceptable to vegans.

How should GPs assess vitamin D deficiency?

Vitamin D is essential for musculoskeletal health. It is required for optimal mineral metabolism and the control of calcium and phosphate homeostasis, it promotes calcium absorption from the bowel, enables mineralisation of newly formed osteoid tissue in bone and plays an important role in muscle function. Rickets in children and osteomalacia in adults are the main manifestations of vitamin D deficiency. Less severe vitamin D deficiency may lead to secondary hyperparathyroidism, bone loss, muscle weakness, falls and fragility fractures in older people.

Who to test for vitamin D deficiency

Vitamin D testing should be prioritised to those patients where the outcome will alter clinical management:

  1. Patients with bone diseases that may be improved with vitamin D treatment

Correcting vitamin D deficiency is essential for patients with osteomalacia and is beneficial for patients with osteoporosis. This does not mean that patients with osteoporosis should undergo routine vitamin D testing. Calcium and vitamin D3 supplementation is common practice in those on treatment for osteoporosis, and testing vitamin D levels in patients where the decision has been made to co-prescribe is unlikely to change patient management.

  1. Patients with bone diseases, prior to specific treatment where correcting vitamin D deficiency is appropriate

Ensuring patients receiving potent antiresorptive osteoporosis treatments (denosumab or zoledronate) are not vitamin D deficient before starting treatment is required to avoid the development of hypocalcaemia.

  1. Patients with musculoskeletal symptoms that could be attributed to vitamin D deficiency

Symptoms of vitamin D deficiency are unfortunately vague and it can be difficult to ascertain whether a low serum 25OHD level is causal or a surrogate marker (e.g. of poor nutrition or a lack of outdoor activity). Nonetheless, if patients are suspected of having symptoms caused by osteomalacia, or have chronic widespread pain, a case can be made to measure vitamin D as part of their clinical and laboratory evaluation.

Who to treat

The recommended definition of deficiency made for adopting into UK practice is:

  • Serum 25OHD
  • Serum 25OHD of 30-50 nmol/L may be inadequate in some people.
  • Serum 25OHD >50 nmol/L is sufficient for almost the whole population.

Following measurement of serum 25OHD it is recommended that patients found to be deficient (

  • fragility fracture, documented osteoporosis or high fracture risk
  • treatment with antiresorptive medication for bone disease
  • symptoms suggestive of vitamin D deficiency
  • increased risk of developing vitamin D deficiency in the future because of reduced exposure to sunlight, religious dress code, dark skin, etc
  • raised parathyroid hormone levels
  • medication with antiepileptic drugs or oral glucocorticoids
  • conditions associated with malabsorption.

In patients whose tests show they have sufficient vitamin D levels (>50 nmol/L) the recommendations are to give lifestyle advice on maintaining adequate vitamin D levels through safe sunlight exposure and diet. For more information, see the Initiation section of this resource

How to treat vitamin D deficiency

The key aims of treatment are:

  • using adequate doses to ensure correction of vitamin D deficiency (to > 50 nmol/L)
  • timely reversal of the clinical consequences of vitamin D deficiency
  • avoiding toxicity.

Oral vitamin D3 is recommended as the treatment of choice in vitamin D deficiency.

Where rapid correction of vitamin D deficiency is required, such as in patients with symptomatic disease or about to start treatment with a potent antiresorptive agent (zoledronate or denosumab), the recommended treatment regimen is based on fixed loading doses followed by regular maintenance therapy:

  • a loading regimen to provide a total of approximately 300,000 IU vitamin D, given either as separate weekly or daily doses over 6 to 10 weeks
  • maintenance therapy comprising vitamin D in doses equivalent to 800-2000 IU daily (occasionally up to 4,000 IU daily), given either daily or intermittently at higher doses.

Where correction of vitamin D deficiency is less urgent and when co-prescribing vitamin D supplements with an oral antiresorptive agent, maintenance therapy may be started without the use of loading doses.

Monitoring patients after treatment

A month after a loading dose of vitamin D has been given, a calcium blood test is recommended to make sure a patient does not have primary hyperparathyroidism. This causes hypercalcaemia which would be exacerbated by the high-dose vitamin D supplement.

Routine follow-up vitamin D blood tests are generally unnecessary unless vitamin D deficiency symptoms continue, a patient has malabsorption problems or it is likely they have not been taking the prescribed supplements.