Vitamin D in the UAE: a sunny country, running low

The UAE has sunshine all year, and vitamin D deficiency is common here. Both statements are true, and the second follows from the first: when the sun is that strong, people avoid it. This post explains what 25-OH vitamin D measures, why so many UAE residents are low, what the number means, and how to raise it without guessing.

What the test measures

Vitamin D is made in skin exposed to UVB light and, to a lesser extent, taken in through food and supplements. The liver converts it to 25-hydroxyvitamin D, which is the storage form and the one a blood test measures. It has a half-life of about 15 days, so the result reflects roughly the last month rather than yesterday.

Results are reported in nmol/L or ng/mL. To convert, divide nmol/L by 2.5.

• Below 30 nmol/L (12 ng/mL) is deficient by every major definition.
• 30 to 50 nmol/L (12 to 20 ng/mL) is insufficient by most.
• 50 to 125 nmol/L (20 to 50 ng/mL) is the range the US National Institutes of Health considers adequate for most people.
• Above 125 nmol/L (50 ng/mL) is where the US National Institutes of Health starts to note possible harm. Toxicity is rare, and usually seen above 375 nmol/L (150 ng/mL).

Why a sunny country is deficient

In a community study of 648 adults in Al Ain, 44% were below 50 nmol/L (20 ng/mL). Of 60,979 patients tested at one Abu Dhabi hospital laboratory between 2012 and 2014, 82.5% were below 75 nmol/L (30 ng/mL). The two figures are not directly comparable: one is a community sample measured against 50 nmol/L, the other hospital patients measured against 75 nmol/L. The reasons are ordinary and cumulative.

• Heat avoidance. From May to October daytime is spent indoors, and movement between places is car to car park to lobby.
• Glass and air conditioning. Window glass blocks UVB. Sun through a window makes no vitamin D at all.
• Clothing. Covered dress, for cultural or sun-protection reasons, leaves little skin exposed.
• Skin tone. Darker skin needs several times longer in the same sun to make the same amount.
• Sunscreen. Sensible for the skin, and it cuts synthesis sharply.
• Body weight. Vitamin D is fat-soluble, and a higher body fat percentage means more of it is stored away from the blood.

What low vitamin D is associated with

The clearest effects are on bone and muscle. Low levels impair calcium absorption, weaken bone over time and are linked with muscle pain, weakness and more falls in older adults. Low vitamin D also shows up alongside low mood, fatigue and worse insulin sensitivity, though in most of those cases the research shows association rather than proven cause, and correcting the deficiency does not reliably fix the symptom. It is worth correcting anyway, because the bone case alone is enough.

Reading it with the rest of the panel

Vitamin D rarely travels alone in a UAE panel. It is worth reading beside:

• Calcium and phosphorus, which vitamin D regulates. A high calcium with a high vitamin D is a reason to speak to a doctor.
• Ferritin and B12, two other nutrition markers that are often read beside it.
• Fasting insulin and HbA1c, given the association with insulin resistance.
• Alkaline phosphatase, which rises when bone is turning over quickly.

Raising it

Sun

There is no simple rule for how much sun is enough. Season, time of day, skin colour and sunscreen all change how much vitamin D the skin makes, and the US National Institutes of Health notes that this makes guidelines on sun exposure difficult, and that limiting exposure is prudent because UV light is the most preventable cause of skin cancer. In summer the heat makes time outdoors impractical, and early morning or late afternoon sun is much weaker in UVB.

Food

Oily fish, eggs and fortified milk help but rarely close a real gap on their own.

Supplements

Whether a supplement is needed depends on your starting level, your weight and your calcium, and that is a conversation for a doctor with your result in front of them.

Retest, then stop guessing

Because 25-OH vitamin D has a half-life of about 15 days, it changes over weeks, and a doctor typically rechecks it when a low level is being treated, to see whether it is improving. A first panel sets the level, and the retest shows whether it has moved. When Clare opens, each result will sit in one account beside the earlier ones, so a change reads as a trend rather than a single number.

Clare is opening with a waitlist at clare.health.