Vitamin D and Calcium: Who Needs Them?

Vitamin D and calcium are among the most widely used supplements, but not everyone needs them, and too much does harm. This article explains where they come from, who is more likely to be deficient, what the test measures, why overdoing it is risky, and why the amount must come from the doctor or pharmacist.

Whenever someone has bone pain or a test says “low vitamin D,” the first answer is usually “take a supplement.” But who, how much and for how long depends on the test and the person’s own situation. In this article we give only the general principles, not amounts.

Where does vitamin D come from?

The NHS writes that most people can make vitamin D from sunlight on the skin in the months when there is enough sun, and BHOF also says most vitamin D comes from the sun. Food contributes less: oily fish, red meat, egg yolk and fortified foods. Supplements exist too.

The NHS says the need for a supplement is greater in people who:

go outside little, for example people who are housebound or disabled or who live in care facilities
cover most of their skin when outdoors
have dark skin, for example those of African, African-Caribbean or South Asian background

BHOF adds that people with celiac disease or inflammatory bowel disease, people who take some anti-seizure medicines, people with obesity, and some older adults are at higher risk.

Where does calcium come from?

The NHS and BHOF both put food first. NHS: dairy, leafy green vegetables such as kale and okra, fortified soy drinks, fortified bread and flour, and fish eaten with its bones. The NHS writes that spinach should not be counted, because the body does not absorb all of its calcium. The NHS says most people can get all the calcium they need from a varied diet.

BHOF says a supplement only fills the gap between food and need, and that if you take calcium pills, absorption is better in smaller doses. Many calcium supplements and multivitamins also contain vitamin D. Check the label before adding another.

Who might need a supplement?

This decision is up to the doctor. The sources say these things:

NHS: A vitamin D supplement is raised for the high-risk groups above, and for other adults only in the low-sun months.
BHOF: Someone who has osteoporosis or low bone density should talk to the doctor about their vitamin D level.
Endocrine Society: Some people need medicine even with enough calcium and vitamin D. Long-term cortisone use and some medicines raise the risk of osteoporosis.

BHOF calls the vitamin D test “25-hydroxy vitamin D” and writes that the doctor can suggest a supplement based on it. The Endocrine Society also says needs differ widely and a blood test can guide the amount.

Too much is risky

Vitamin D: The NHS writes that high, long-term intake can raise blood calcium, called hypercalcemia, and this weakens bone and damages the kidneys and heart. You cannot be poisoned by sunlight. The NHS sets a daily upper limit that differs by age. We do not write amounts, because they must be set with the doctor or pharmacist.
Calcium: BHOF writes that extra calcium has no benefit and can cause constipation, kidney stones and possibly calcification of the heart. The NHS says very high intake causes abdominal pain and diarrhea.
Combination: MedlinePlus names too much vitamin D and too much calcium supplement together with vitamin D among the causes of high calcium, along with dehydration, an overactive parathyroid and some medicines. So “the more the better” is not correct.

I have high calcium or an overactive parathyroid. What should I do?

If your calcium test is high, talk to the doctor before starting any supplement. NIDDK writes that in an overactive parathyroid vitamin D is often low and a supplement may be given, but there is no need to limit dietary calcium. The NHS says not to change your diet to lower calcium without a specialist’s opinion. That means you should neither increase the supplement nor cut the food on your own.

Calcium supplements and thyroid pills

The NHS writes that calcium and iron supplements may not be compatible with levothyroxine. Ask the pharmacist or doctor for the exact spacing.

Simple points

Food first. Take a supplement to fill a gap, not instead of food.
Do not take the amount from the internet or a neighbor. Ask the doctor or pharmacist.
Before a blood test, say so if you take a multivitamin or a hair and nail supplement (which contains biotin).
Weight-bearing activity, quitting smoking and cutting back on alcohol help bone (NHS and Endocrine Society).
If you have had a fracture from a minor knock after age 50, ask about bone density. See the page “Osteoporosis, Calcium and the Parathyroid.”
See the life-threatening signs of high or low calcium in the guide “When should I call right away?”