SalamatYar
Vitamin D deficiency is one of the most common nutritional deficiencies in adults, especially in people who get less direct sunlight. According to some global estimates, nearly one billion people worldwide have insufficient or deficient vitamin D levels — even in regions with plenty of sun.
Unit: nanograms per milliliter (ng/mL) for 25-hydroxy vitamin D
Why is it so common?
Our body makes a large part of its vitamin D when sunlight hits the skin. Modern lifestyles — working indoors, using sunscreen and covering the whole body — have left many people deficient, even in sunny regions.
Who is most at risk?
- People over 65; the skin's ability to make vitamin D declines with age
- People with darker skin; more melanin reduces vitamin D production from sunlight
- People who are overweight or obese
- Exclusively breastfed infants who do not receive a supplement
- People with digestive diseases that impair fat absorption, such as Crohn's disease, celiac disease and cystic fibrosis
- People who have had weight-loss surgery (gastric bypass)
- People with chronic kidney or liver disease
- People with little sun exposure: living at northern latitudes, winter season or being housebound
Natural sources of vitamin D
Only a few foods naturally contain significant vitamin D: fatty fish such as salmon, tuna and trout; egg yolks; and dairy products, plant milks and breakfast cereals that have been fortified with vitamin D.
Besides diet, 10 to 15 minutes of direct midday sun exposure (without sunscreen), a few times a week, can increase the skin's natural production of vitamin D; however, this should always be weighed against the risk of sunburn and skin cancer.
Possible symptoms
Chronic fatigue, bone and muscle pain, general weakness and low mood are common symptoms — although in many people the deficiency causes no symptoms at all and is only revealed by a blood test.
Reference range and supplements
A level above 30 ng/mL is usually considered sufficient; 20 to 29 is insufficient and below 20 is deficient. If your level is lower, your doctor may prescribe a supplement dose and duration based on the severity of the deficiency — never decide the dose on your own, because taking too much vitamin D can also cause problems.
If you belong to one of the high-risk groups above or experience symptoms such as persistent bone pain, significant muscle weakness or (in older adults) more frequent falls, discuss a 25-hydroxy vitamin D blood test with your doctor.
Frequently asked questions
Is a vitamin D test recommended for everyone?
No, not necessarily. Some scientific bodies do not consider the evidence sufficient for routine vitamin D screening in people without symptoms, but for high-risk people or those with symptoms, testing is reasonable.
Does sunlight through glass also make vitamin D?
No. The UVB rays needed to make vitamin D are filtered out by window glass, so you need to be in direct sunlight outdoors.
Is it possible to take too much vitamin D?
Yes, although it is rare. Long-term use of very high doses can cause a dangerous rise in blood calcium and problems such as nausea, weakness and kidney problems; for this reason the dose should be determined under a doctor's supervision.
How long does it take to correct vitamin D deficiency with a supplement?
Depending on the severity of the deficiency and the prescribed dose, retesting after 8 to 12 weeks of regular supplement use is usually recommended to check the improvement in blood level.