Vitamin D is called the “sunny” vitamin because your body produces it when sunlight hits your skin. About 90 percent of the vitamin D people need comes from sunlight. The rest comes from foods that contain it or from supplements.
In recent years, researchers have warned that vitamin D supplements aren’t right for everyone. In some cases, high doses of these supplements are toxic, especially for young children and older adults.
Researchers say that because vitamin D has become so popular, it’s vital to let people know how to dose it correctly and what side effects can occur.
Scientists haven’t settled on the exact doses of the “sunny vitamin” that are dangerous. One thing is clear: our bodies need to get vitamin D. It:
- helps the body absorb calcium
- supports immune function
- helps with cell renewal
- regulates metabolism
- maintains neuromuscular function
Meanwhile, long-term vitamin D deficiency raises the risk of developing diseases in several systems:
- neurological diseases
- autoimmune diseases
- bone diseases
- cardiovascular diseases
Hypercalcemia: When Vitamin D Backfires
Excessive buildup of vitamin D in the body causes intoxication (or hypervitaminosis), which leads to calcium deposits in the arteries, kidneys, blood vessels, lungs, and even the heart — a condition called hypercalcemia.
Critically high calcium levels are extremely dangerous because they:
- promote the formation of calcium deposits
- disrupt bone metabolism
- cause nausea, vomiting, constipation, fatigue, muscle weakness, and bone pain
Most people recover from vitamin D intoxication after they stop taking the supplements and receive intravenous fluids to lower their blood calcium levels. However, without treatment, hypercalcemia can sometimes lead to kidney failure, said Carly Cassella, an expert at Science Alert.
Some researchers even suggest that older adults with high blood levels of vitamin D are more prone to falls.
Sun, Food, or Supplements — Where to Get Your Vitamin D
Besides sunlight, which provides the bulk of the vitamin D we use, good dietary sources exist.
Those include:
- fatty fish — salmon, herring, trout, mackerel, sardines, tuna
- cod liver and cod liver oil
- fortified dairy products — milk, yogurt, cheese, butter
- wild mushrooms that grew in the sun
- chicken and quail egg yolks
- red caviar
Whether vitamin D supplements are as beneficial as dietary sources remains controversial. Some scientists suggest that these supplements can slow aging, improve cognitive function, and ease depression symptoms, while other researchers question their effectiveness.
Research shows that vitamin D intoxication most often results from incorrect use of supplements. In 2016, the Danish Health Authority withdrew from the market a supplement that contained 75 times the dose of vitamin D recommended by doctors.
Recently, scientists at Harvard Medical School published an article advising people with vitamin D deficiency to start by getting vitamin D from fortified foods. Those foods are far less likely to cause toxicity than supplements.
Of course, supplements can be the only practical source of vitamin D for some people who lack sun exposure or access to vitamin-D–rich foods. In those cases, consult a doctor about the right supplement dose.
Photo: Openverse
