Vitamin D

What is it?

Vitamin D helps the body absorb calcium, which builds strong bones and helps prevent osteoporosis; the body also needs it for muscle movement, nerve signalling and the immune system's defence against bacteria and viruses (ODS).

It regulates the calcium and phosphate that bones, teeth and muscles need (NHS), and it is called the 'sunshine vitamin' because the skin makes it when exposed to the sun (MedlinePlus).

Sunlight

• Bare skin makes it from sunlight; clouds, smog, older age and darker skin reduce this, window glass blocks it and sunscreen limits it (ODS).

Food

• Few foods contain it naturally: oily fish such as salmon, tuna and mackerel, fish liver oils, and small amounts in beef liver, egg yolks, cheese and mushrooms; some foods such as milk and breakfast cereals are fortified, and fortification differs between countries (ODS and NHS).

Supplements

• Two forms, D2 and D3, both raise blood levels; D3 may raise them more and for longer. It is absorbed best with a meal that contains some fat (ODS).

Why it matters

Deficiency causes rickets in children — soft, weak, deformed and painful bones — and osteomalacia in teens and adults, with bone pain and muscle weakness (ODS). It can also cause osteoporosis in adults (MedlinePlus).

Signs of rickets and osteomalacia include bowed legs in children, swollen painful wrists, pain in the back, shoulders, ribs, pelvis or legs, muscle weakness, a change in walking, difficulty with stairs, bones that break easily, and short stature and late teeth in children (NHS).

The Saudi Ministry of Health describes rickets as common and advises mothers to continue breastfeeding.

Key points

• Sun alone may not be enough in the Gulf: a 2019 review reports high rates of deficiency in the Gulf Cooperation Council countries despite plentiful sunshine, linked to habits that limit sun exposure, covering clothing, skin colour, age and obesity.
• Routine vitamin D testing is not recommended for everyone; it is ordered when a problem is suspected or for people at higher risk (MedlinePlus).
• Vitamin D toxicity does not come from the sun but from too many supplements (ODS and NHS).
• A breastfed baby needs a supplement, because breast milk alone does not provide enough (ODS).
• Official sources do not support using it for weight loss or to prevent depression or diabetes (ODS).

Recommended daily amounts

The UK NHS recommends 10 micrograms a day for everyone aged 1 and over, including pregnant and breastfeeding women, 8.5 to 10 micrograms for babies up to 1 year, and taking it all year for people who are rarely outdoors or who cover most of their skin outdoors. (1 microgram = 40 IU.)

These are nutritional reference values for healthy people as their sources publish them, not doses for treating deficiency; the doctor decides on treatment and its dose, and some medical conditions make the safe limit lower (NHS).

The vitamin D test

The test usually measures 25-hydroxyvitamin D in the blood, the most accurate way to see whether you have enough. No special preparation is needed, and the sample is taken from the arm in less than five minutes (MedlinePlus).

Cut-offs differ between laboratories and studies; many studies in Arab countries define deficiency as below 20 ng/mL and sufficiency as 30 ng/mL or more (Eastern Mediterranean Health Journal), so rely on your laboratory report and your doctor.

Special groups

Groups more likely to be low:

• Breastfed babies (ODS).
• Older adults, because the skin makes less with age (ODS).
• People who seldom expose their skin to the sun, including those who cover most of their skin outdoors and those rarely outdoors (ODS and NHS).
• People with darker skin: the darker the skin, the less vitamin D it makes (ODS).
• People with conditions that limit fat absorption, such as Crohn's disease, coeliac disease and ulcerative colitis, and people with obesity or after gastric bypass (ODS).
• People with kidney or liver disease and people taking medicines such as steroids (MedlinePlus).
• Pregnant women; the Saudi Ministry of Health lists pregnancy as a risk factor for rickets, and the NHS advises a supplement in pregnancy and breastfeeding.

In the Gulf, a 2019 review reports levels below 20 ng/mL in 81% of the groups studied in Saudi Arabia, deficiency or insufficiency in up to 82.5% of 60,979 patients in the UAE, and inadequacy in about 86% of Qatar Biobank participants. These are study figures with different definitions, not a single population survey.

Risks and cautions

Taking too many supplements for a long time can raise blood calcium, weakening bones and damaging the kidneys and heart (NHS). Blood levels above 375 nmol/L (150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, passing a lot of urine, thirst and kidney stones; extremely high levels can cause kidney failure, an irregular heartbeat and even death (ODS).

Interactions: orlistat reduces its absorption, prednisone can lower its level, some statins may work less well with high amounts of it, and thiazide diuretics with vitamin D supplements can raise calcium too high; tell your doctor about every supplement you take (ODS).

Limits of this information

What does the evidence say? According to ODS, vitamin D with calcium slightly increases bone strength in older adults, but it is unclear whether it reduces falls or fractures; it does not appear to lower the risk of breast, colorectal or lung cancer or heart disease, does not prevent depression, does not improve blood sugar and does not help weight loss.

There is not enough evidence to take it solely to prevent or treat COVID-19 (NHS).

A 2026 systematic review in the Eastern Mediterranean Health Journal found an association between vitamin D deficiency and metabolic syndrome in Arab countries, but the evidence is observational and of low certainty, so it does not show that deficiency is the cause.

The NHS guidance on time in the sun is specific to the UK, and the sources of this page give no equivalent for the Gulf or for people who wear covering clothing. The sources also give no doses for treating deficiency; that is the doctor's decision.

Common questions