Vitamin D
Vitamin D is a fat-soluble vitamin that supports calcium absorption, bone mineralization, muscle function, and immune-related processes.
Overview
Biological role
Vitamin D promotes calcium and phosphorus absorption, supports bone mineralization, helps maintain serum calcium and phosphate, and contributes to muscle and immune function.
Mechanism of action
Vitamin D is converted in the liver to 25-hydroxyvitamin D and in the kidney and other tissues to active 1,25-dihydroxyvitamin D, which binds the vitamin D receptor and regulates calcium-phosphate homeostasis and gene expression.
Chemical forms
Vitamin D3 as cholecalciferol; vitamin D2 as ergocalciferol; circulating 25-hydroxyvitamin D; active 1,25-dihydroxyvitamin D. Fat-soluble vitamin; status depends on sunlight, diet, supplements, fat absorption, liver/kidney activation, and health context.
Quick answers before choosing a supplement
Chemical forms and absorption
Common forms
Vitamin D3 as cholecalciferol; vitamin D2 as ergocalciferol; circulating 25-hydroxyvitamin D; active 1,25-dihydroxyvitamin D. Fat-soluble vitamin; status depends on sunlight, diet, supplements, fat absorption, liver/kidney activation, and health context.
Absorption context
Because vitamin D is fat-soluble, absorption improves when taken with a meal containing fat.
Clinical use
Vitamin D testing and supplementation should be interpreted with clinical context. Supplementation corrects deficiency; broad claims beyond skeletal outcomes vary by condition and baseline status.
Absorption and action pathway
What to take with, and what to avoid
Works Well With
Avoid / Use Caution
Best time to take
Frequently asked questions
When is the best time to take Vitamin D?
Take consistently; fat-soluble vitamins are usually best with a meal that contains fat, while water-soluble vitamins are usually flexible.
Can Vitamin D be taken with coffee or milk?
It depends on the vitamin. Fat-soluble vitamins are best with food; water-soluble vitamins are generally more flexible.
Who should be careful with Vitamin D?
Higher deficiency risk occurs with limited sun exposure, darker skin, older age, fat malabsorption, bariatric surgery, exclusive breastfeeding without supplementation, and some restrictive diets.
Food and Intake
| Age / group | Male | Female | Pregnancy | Lactation | Upper limit |
|---|---|---|---|---|---|
| 1-3 years | 15 | 15 | – | – | UL 63 |
| 4-8 years | 15 | 15 | – | – | UL 75 |
| 9-18 years | 15 | 15 | 15 | 15 | UL 100 |
| 19-70 years | 15 | 15 | 15 | 15 | UL 100 |
| >70 years | 20 | 20 | – | – | UL 100 |
International reference intake comparison
| Country / authority | Common reference value |
|---|---|
| USA / NIH-FNB | RDA 15 mcg age 1-70 years, 20 mcg >70 years; UL 100 mcg |
| Europe / EFSA | AI 15 mcg assuming low sun exposure |
| Australia-New Zealand / NRV | AI adults 5-15 mcg by age; higher in older adults |
| Thailand / Thai FDA | Thailand: use Thai RDI and Thai FDA / Ministry of Public Health regulations for labeling and supplement products. Do not interpret labeling values as therapeutic doses; product-specific limits must be checked against the latest notification and formula. |
This table compares reference-intake frameworks across authorities. Values may use different terms such as RDA, AI, PRI, or NRV and should not be merged into one universal dose.
Food source comparison for Vitamin D
| Food | Serving amount | Vitamin D | %DV | %DV bar | Servings to reach 20 mcg |
|---|---|---|---|---|---|
| cod liver oil | 1 tablespoon | 34 mcg | 170% | 0.6 | |
| cooked trout | 3 oz | 16.2 mcg | 81% | 1.2 | |
| sockeye salmon | 3 oz | 14.2 mcg | 71% | 1.4 | |
| UV-exposed mushrooms | 1/2 cup | 9.2 mcg | 46% | 2 | |
| vitamin D-fortified milk | 1 cup | 2.9 mcg | 14% | 7 | |
| egg | 1 egg | 1.1 mcg | 6% | 18 |
Food values are practical comparison values. Actual content varies by variety, preparation, fortification, and serving size.
Safety
Deficiency
Deficiency causes rickets in children and osteomalacia in adults and can contribute to low calcium, secondary hyperparathyroidism, bone pain, and muscle weakness.
Excess and toxicity
Toxicity is usually caused by excessive supplement intake and can produce hypercalcemia, nausea, vomiting, weakness, kidney stones, and renal injury.
Precautions
People with granulomatous disease, lymphoma, primary hyperparathyroidism, kidney disease, or high calcium should use vitamin D under clinical supervision.
Special populations
Higher deficiency risk occurs with limited sun exposure, darker skin, older age, fat malabsorption, bariatric surgery, exclusive breastfeeding without supplementation, and some restrictive diets.
Fast risk map
LOW: insufficient intake
Deficiency causes rickets in children and osteomalacia in adults and can contribute to low calcium, secondary hyperparathyroidism, bone pain, and muscle weakness.
UL: excess intake
Toxicity is usually caused by excessive supplement intake and can produce hypercalcemia, nausea, vomiting, weakness, kidney stones, and renal injury.
Precautions: interactions and timing
People with granulomatous disease, lymphoma, primary hyperparathyroidism, kidney disease, or high calcium should use vitamin D under clinical supervision.
SP: special populations
Higher deficiency risk occurs with limited sun exposure, darker skin, older age, fat malabsorption, bariatric surgery, exclusive breastfeeding without supplementation, and some restrictive diets.
Interactions and Clinical Context
Drug interactions
ODS lists interactions with orlistat, statins, steroids, and thiazide diuretics. Thiazides plus vitamin D may increase hypercalcemia risk in susceptible people.
Food interactions
Because vitamin D is fat-soluble, absorption improves when taken with a meal containing fat.
Clinical notes
Vitamin D testing and supplementation should be interpreted with clinical context. Supplementation corrects deficiency; broad claims beyond skeletal outcomes vary by condition and baseline status.
Evidence level
High for bone physiology, deficiency disease, RDA, and toxicity; variable for nonskeletal outcomes.