- People who can't properly absorb fat (fat malabsorption)
Vitamin D requires some dietary fat in order to be absorbed in the small intestine. People with conditions that cause fat malabsorption, such as cystic fibrosis, celiac disease, Crohn's disease, whipple disease, and chronic liver disease, are more prone to vitamin D deficiency. People with kidney disease may not be able to convert vitamin D to its active form.
- People who are obese
- Infants who are exclusively breastfed
Vitamin D requirements for infants can't be met by human breast milk alone. Consult your pediatrician before using vitamin D supplements in infants.
Vitamin D is a fat-soluble vitamin. This means that, if consumed in excess, it can build up in the body and cause toxic symptoms, unlike vitamin C and other water-soluble vitamins. Because the buildup is slow, it can take months or years before toxic levels are reached.
Too much vitamin D can result in high levels of calcium in the blood (hypercalcemia), which can lead to calcium deposits in soft tissues such as the lungs or heart, confusion, kidney damage, kidney stones, nausea, vomiting, constipation, weight loss, and poor appetite.
Possible Drug Interactions
The combination of vitamin D and calcium should not be taken with thiazide diuretics, because it could lead to excess calcium levels in the body. People taking calcium-channel blockers should not take vitamin D and calcium, unless under a doctor's supervision, because it may interfere with the effect of the medication.
Anti-seizure medications and rifampin (for tuberculosis) may reduce vitamin D levels.
People with low parathyroid function may be at higher risk of high blood calcium levels while taking vitamin D.
Steroids, laxatives, and cholesterol-lowering drugs may reduce the amount of vitamin D your body can absorb. Ideally, vitamin D should be taken several hours before or after consuming these drugs.
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