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What are the Causes of Low and High Vitamin D Levels?
Low vitamin D is primarily caused by insufficient sunlight exposure, poor dietary intake, or gut malabsorption; whilst high levels almost exclusively result from over-supplementation.
The liver and kidneys are responsible for converting vitamin D into its active form that the body can use. Impaired function in these organs can cause a deficiency.
Causes of Low Vitamin D Levels (Deficiency)
- Lack of Sun Exposure: Because the body produces vitamin D when bare skin is exposed to UVB rays, spending most of your time indoors, living at high latitudes with long winters, or overusing sunscreen limits production.
- Darker Skin Pigmentation: Higher levels of melanin act as a natural sunscreen, meaning people with dark brown or black skin require significantly more sun exposure to produce the same amount of vitamin D as lighter-skinned individuals.
- Malabsorption Disorders: Conditions that affect the small intestine, such as Coeliac disease, Crohn’s disease, and Ulcerative Colitis (UC), prevent the gut from absorbing fat-soluble vitamins.
- Obesity: Vitamin D is fat-soluble and gets trapped in body fat tissue, which lowers the amount circulating in your bloodstream.
- Chronic Kidney Disease (CKD) and Chronic Liver Disease (CLD): Vitamin D deficiency affects the vast majority of Chronic Kidney Disease (CKD) and CLD patients.
- Age: Older adults are less efficient at synthesising vitamin D in the skin upon sun exposure.
Causes of High Vitamin D Levels (Toxicity)
- Supplement Overuse: Hypervitaminosis D is almost always caused by taking excessively high doses of vitamin D supplements or prescription medications without medical supervision.
- Medical Conditions: Rarely, certain granulomatous diseases (like sarcoidosis or tuberculosis) and specific lymphomas can cause white blood cells to overproduce active vitamin D.
- Medications: Certain drugs, such as thiazide diuretics (for high blood pressure) or prolonged use of antacids, can cause an increase in blood vitamin D or calcium levels.
Note: You cannot get vitamin D toxicity from sun exposure or a typical diet, as the body regulates and limits how much it produces from sunlight.
