Vitamin D is the most common global nutritional deficiency and a very important vitamin for men enhancement. About one-quarter of the UK population has a vitamin D deficiency, growing to about one-third in the winter months.1 The primary source of vitamin D comes from sunlight. It’s also present in specific foods (e.g. cod liver oil, oily fish, egg yolk, milk, mushrooms), but having enough vitamin D from diet alone is very difficult. Vitamin D facilitates calcium absorption from the gastrointestinal tract and helps mineralize the bone. The principal consequence of adult vitamin D deficiency is osteomalacia, where osteoclasts break down the bone to increase serum calcium. Various claims have been made about the value of vitamin D in chronic fatigue syndrome, reproductive health, various diseases, and macular degeneration, but there is insufficient evidence to support these claims.

1. Know the causes and risk factors

Sunlight is important but bear in mind other causes and risk factors. Vitamin D derived from diet or sunlight is inactive and is transformed into the active metabolite 1,25-dihydroxyvitamin D in both the liver and the kidney. Renal conversion is promoted by parathyroid hormone. Knowing about conversion makes it easy to remember the following categories of risk factors for vitamin D deficiency (see Box 1).
Box 1: Risk factors for vitamin D deficiency
Reduced intake due to diet or lack of sun exposure
restricted diet (e.g. vegan)
malabsorption (e.g. coeliac, post bariatric surgery)
reduced sun exposure (e.g. rarely leaving the house or covering skin when outside)
age over 65 years (the amount of substrate in the skin from which vitamin D is synthesised reduces with age)
darker skin (melanin absorbs some ultraviolet B light so people with dark skin need more sunlight than people with lighter skin to produce the same amount of vitamin D)

  • Reduced liver conversion
  • chronic liver disease
  • induction of liver enzymes
  • Reduced renal conversion
  • chronic renal failure
  • nephrotic syndrome
  • reduced parathyroid hormone
  • Increased demand of vitamin D
  • pregnancy
  • breastfeeding.

2. Recommend vitamin D supplementation

Public Health England (PHE) has recommended that almost everyone in the UK will take a 10 mcg (400 IU) vitamin D supplement in the autumn and winter months2,3 since there is not enough sunshine at this time of year to produce enough vitamin D. The only exception is babies under the age of 1 who drink at least 500 ml of formula daily, because formula is enriched with vitamin D. Babies under the age of 1 who are breastfed should receive a supplement of 8.5–10 mcg.3 Those who have very little sun exposure (e.g. those in care homes or who cover all their skin outside) should take a supplement throughout the year.

3. Do not offer routine tests

The majority of people don’t need a vitamin D test. NICE advises that clinicians should not check routinely for levels of vitamin D. Tests should only be performed if there is an indication to do so, including (in adults aged over 18 years):1

  • a suspicion of osteomalacia (bony pain, muscle aches and weakness, impaired physical function, waddling gait, symmetric lower back pain)
  • chronic widespread pain
  • the individual has had a fall
  • symptoms of hypocalcaemia (e.g. muscle cramps, numbness)
  • a bone disease that may be improved with vitamin D treatment (e.g. osteoporosis, Paget’s disease).

Indications for testing kids include:

  • Ricket concern (bow legs, knock knees, delayed tooth eruption, painful wrist swelling)
  • unexplained bony pain or muscle weakness
  • chronic disease that may increase the risk of deficiency of vitamin D (e.g. anything that triggers malabsorption);

4. Recognise deficiency from insufficiency

NICE recognizes that there is no clear consensus on when to diagnose vitamin D deficiency or insufficiency, and that criteria that differ between laboratories; however, the National Osteoporosis Society (NOS),5 NICE1 and the Institute of Medicine6 have settled on acceptable thresholds for determining vitamin D status
PHE study on vitamin D supplementations2 told the Scientific Advisory Committee on Nutrition that the likelihood of skeletal ill health is increased by less than 25 nmol / l vitamin D3, but the difference is unlikely to make any significant difference to the management of vitamin D deficiency in the real world.

5. Prescribe a loading dose to treat vitamin D deficiency

A loading dosage of approximately 300.000 IU of vitamin D.1 should be recommended for people with vitamin D deficiency. This may be achieved in several forms, including: 1 • 50 000 IU once weekly for six weeks.
Note that these high doses are not available and must be administered over the counter.

6. Repeat blood tests after initial treatment

Calcium levels should be checked 1 month after the end of the treatment course. Hypercalcaemia should raise suspicion that the patient has primary hyperparathyroidism; the patient should not take any more vitamin D and appropriate investigations should be instigated.

  • NOS suggests regular monitoring unless the patient has malabsorption, remains symptomatic or is likely to have low adherence5
  • NICE recommends re-checking vitamin D levels within 3–6 months of the loading dose (as long as it takes at least 3 months to stabilize vitamin D levels).1 When vitamin D levels do not improve despite good adherence or the patient remains symmetrical.

    7. Direct patients to over-the-counter supplements

    Vitamin D supplements can most people buy over the counter and do not need monitoring routine. People who have vitamin D insufficiency, and people with deficiency who have completed their loading dose, should take a maintenance dose of 800 IU per day (or 2000 IU, occasionally up to 4000 IU, for people with malabsorption disorders).1 Vitamin D is very cheap to buy over the counter and some CCGs recommend that healthcare professionals should refrain from prescribing vitamin D maintenance preparations, and encourage patients to buy their dose instead.7 For the children of families on a low income, Legal, without a prescription need to have a way to obtain vitamin D.
    The maintenance dose should be taken for life for patients.1 Regular tests on the vitamin D maintenance dose are not needed.

    8. Remind patients about sunscreen

    Exposure to the sun constitutes an important risk factor for melanoma, especially where a patient has been sulphurized in the past and major public-health initiatives have taken place in order to increase awareness of the need for a sunscreen8. Patients should be advised to obtain sufficient vitamin D by spending short sunscreen-free periods in summer, but for longer exposure the sunscreen is still advisable. Those who can not expose their skin to the sun will take supplements throughout the year. The risk of melanoma production is raised by about 20% by the sunbeds and should not be used therefore.

    9. Be aware of the symptoms of vitamin D toxicity

    Toxicity to vitamin D is uncommon, and is usually found only in people who use high doses for longer periods of time, but the effects should be recognized by healthcare professionals. Hypercalcaemia (eg nausea, diarrhea, bowel habit changed, weight loss, fatigue, headache) caused symptoms. Vitamin D toxicity is associated with serum levels of at least 300 nmol / l, and usually above 600 nmol / l; it is very unlikely that a 300,000 IU loading dose, or subsequent maintenance dose would cause toxicity.

    10. Do not forget lifestyle advice

    So far this article has concentrated on how GPs can treat patients with vitamin D deficiency or insufficiency, but many patients are willing to help themselves by making lifestyle changes. Patients should be advised to optimise their dietary intake of vitamin D and calcium — downloadable information sheets (such as the British Dietetic Association’s Food Fact sheet on vitamin D, can be helpful. Obesity is a risk factor for vitamin D deficiency, possibly because vitamin D (which is fat-soluble) is sequestered in adipose tissue and so is less bioavailable. It would therefore be reasonable to advise weight loss, particularly in people with a body mass index of over 30 kg/m2.