Where Do We Get Vitamin D From?
The body can make vitamin D when skin is exposed to sunlight. This is why vitamin D is often called the “sunshine vitamin.” But sunlight is not always enough. The amount of vitamin D your body makes depends on the season, time of day, where you live, cloud cover, skin tone, clothing, sunscreen use, and how much time you spend outdoors.
Food can also provide vitamin D, but naturally rich food sources are limited. Harvard’s Nutrition Source lists fatty fish, fish liver oils, egg yolks, cheese, beef liver, UV-exposed mushrooms, and fortified foods such as some cereals and milks as sources of vitamin D.
This is why some people use supplements, especially during months when sunlight is weaker. The NHS says that from autumn and winter, people may need vitamin D from food or supplements because sunlight may not be strong enough for the body to make enough vitamin D.
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Caption: Sunlight, food, and supplements are the main sources of vitamin D.
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Why Do So Many People Take Vitamin D Supplements?
Many people take vitamin D because they do not get enough sunlight, live in colder climates, spend most of the day indoors, or have been told by a doctor that their vitamin D level is low.
Some groups may be more likely to have low vitamin D levels. Mayo Clinic notes that older adults, breastfed babies, people with Black or brown skin, people with obesity, people who have had gastric bypass surgery, and people with conditions that affect fat absorption may have a higher risk of not getting enough vitamin D.
A blood test is one of the best ways to know if someone is getting enough vitamin D. The NIH explains that vitamin D status is usually measured through a blood test for 25-hydroxyvitamin D.
This is important because guessing can be misleading. Feeling tired does not automatically mean someone has low vitamin D. At the same time, taking a high-dose supplement without testing can increase the risk of taking more than the body needs.
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Caption: A blood test can help show whether vitamin D levels are low, adequate, or too high.
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The Main Warning: Too Much Vitamin D Can Be Harmful
The biggest risk of taking too much vitamin D is a buildup of calcium in the blood, called hypercalcemia. The NHS warns that taking too many vitamin D supplements over a long period can cause too much calcium to build up in the body, which may weaken bones and damage the kidneys and heart.
Mayo Clinic also explains that vitamin D toxicity is usually caused by taking large doses of vitamin D supplements, not by normal food intake or sunlight.
This means the danger usually comes from supplement misuse. For example, someone may take a high-dose vitamin D pill every day without realizing it is meant to be taken weekly or only for a short period. Another person may take several products at the same time, such as a multivitamin, a bone health supplement, and a separate vitamin D capsule, and accidentally combine too much.
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Caption: Taking several supplements at once can accidentally increase total vitamin D intake.
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How Much Vitamin D Is Too Much?
The exact amount a person needs depends on age, health, diet, sunlight exposure, and medical advice. But there are widely used safety limits.
The NHS says adults, pregnant and breastfeeding women, older adults, and children aged 11 to 17 should not take more than 100 micrograms, or 4,000 IU, of vitamin D per day unless advised by a doctor. The NHS also states that children aged 1 to 10 should not have more than 50 micrograms, or 2,000 IU, per day, and infants under 12 months should not have more than 25 micrograms, or 1,000 IU, per day.
In the United States, Mayo Clinic states that most adults need about 600 IU daily, while adults over 70 need about 800 IU daily. It also warns not to take more than 4,000 IU per day unless a healthcare professional tells you to.
One detail that confuses many people is the difference between mcg and IU. The NHS explains that 1 microgram of vitamin D equals 40 IU, so 10 micrograms equals 400 IU.
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Caption: Vitamin D labels may show dosage in micrograms, IU, or both.
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Warning Signs of Too Much Vitamin D
Vitamin D toxicity can lead to high calcium levels, and high calcium can affect different parts of the body. Mayo Clinic lists possible effects of vitamin D toxicity such as stomach upset, vomiting, weakness, frequent urination, bone pain, kidney stones, and kidney trouble.
The NIH also lists symptoms linked with high calcium from vitamin D toxicity, including nausea, vomiting, muscle weakness, loss of appetite, dehydration, excessive thirst, frequent urination, pain, and kidney stones.
These symptoms can have many causes, so they do not automatically mean vitamin D toxicity. But if someone is taking high-dose vitamin D and develops unusual symptoms, they should contact a healthcare professional.
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Caption: Unusual symptoms while taking high-dose supplements should be checked by a professional.
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