Uncontrolled vitamin D supplement use can cause poisoning, Turkish expert warns

By Duygu Yener and Gizem Nisa Demir

Uncontrolled use of vitamin D supplements can lead to poisoning and serious health complications, a Turkish endocrinology expert warned, stressing the risks of excessive and unsupervised intake.

Prof. Dr. Mustafa Altay, an endocrinology and metabolic diseases specialist at the University of Health Sciences Ankara Training and Research Hospital, told Anadolu that vitamin D levels above a certain threshold pose significant dangers.

“When the vitamin D level exceeds 100 nanograms per milliliter, there is a risk of vitamin D poisoning,” Altay said.

Speaking about vitamin D deficiency and the rising use of supplements, particularly during winter months, Altay explained that vitamin D production decreases in autumn and winter because sunlight does not reach the Earth at suitable angles.

As a result, individuals who do not have sufficient vitamin D stores may develop deficiency or insufficiency. Altay said a blood vitamin D level of 30 to 50 ng/mL is adequate for musculoskeletal health in healthy adults.

“If the measured vitamin D level is between 12 and 20 ng/mL, we consider it vitamin D insufficiency. If it is below 12 ng/mL, we define it as vitamin D deficiency,” he said.

Altay warned that excessive intake can be dangerous, noting that vitamin D accumulates in the body and cannot be easily excreted.

“Once the vitamin D level exceeds 100 ng/mL, the risk of poisoning increases. Excessive and uncontrolled intake can lead to toxic effects,” he added.

- Do not confuse treatment with supplementation

Altay said symptoms of vitamin D deficiency are more common among people with limited sun exposure, particularly those who work indoors.

“These individuals may experience fatigue, muscle weakness, difficulty walking, and muscle and bone pain,” he said, adding that long-term and severe deficiency can lead to osteoporosis and bone fractures.

He noted that fatty fish such as tuna, mackerel and salmon, as well as butter, egg yolk, liver and sun-dried mushrooms, are natural sources of vitamin D, but emphasized that diet alone is usually insufficient.

“If adequate sun exposure is not possible, supplements can be used. However, these are not medication-level doses,” Altay said.

“We prescribe vitamin D treatment in individualized doses only in cases of deficiency or insufficiency. Treatment and supplementation should not be confused,” he added.

- Poisoning risk higher in elderly, children and women

Altay underlined that vitamin D poisoning is rare when the vitamin is produced naturally through sunlight or obtained from food, but is most commonly caused by excessive use of supplements.

“Sometimes people take very high doses or use supplements for long periods without medical supervision,” he said.

He noted that the tolerable upper daily intake limit for vitamin D is 4,000 international units.

“A single dose above 40,000 units or long-term use exceeding 4,000 units daily can raise vitamin D levels to toxic ranges,” Altay said, adding that poisoning is seen most often in elderly individuals, young children and women.

- High calcium levels an early warning sign

Altay said the first sign of vitamin D poisoning is elevated calcium levels in the blood.

“This can cause nausea, vomiting, frequent urination, dehydration, fatigue and muscle weakness,” he said.

“In more severe cases, kidney stones, acute kidney injury, heart rhythm disorders, palpitations, and neurological or psychiatric symptoms such as confusion, depression and even coma may develop. Some cases can become life-threatening.”

He stressed that in suspected poisoning cases, vitamin D and calcium intake should be stopped immediately and medical attention sought.

“Depending on the clinical condition, hospitalization and treatment may be required,” he said, adding that public awareness, guideline-based supplement use and medical follow-up are essential to prevent poisoning.

Altay also noted that elderly people, individuals with obesity, those working indoors, patients with osteoporosis, malabsorption disorders, chronic diseases, or those using certain medications are at higher risk of vitamin D deficiency.

He said vitamin D levels in these groups should be measured under medical supervision, particularly in autumn and winter.

For individuals outside risk groups, Altay said routine testing and supplementation are not necessary, noting that there is insufficient scientific evidence showing additional health benefits for people with normal vitamin D levels.

- Best timing for sun exposure

Altay explained that in Türkiye, sunlight is suitable for vitamin D production between March and October.

He recommended going outdoors three to four days a week between 10 am and 4 pm, adding that 10 to 15 minutes of sun exposure may be sufficient for people with fair skin, while those with darker skin may need up to 35 minutes.

Hands, arms, face or legs should be directly exposed to sunlight, he said.

He also warned that sunscreens with a protection factor of 15 or higher block UV-B rays needed for vitamin D production.

“Exposure beyond recommended durations can increase the risk of skin cancer,” Altay cautioned.