Vitamin D side effects

The main side effect of too much vitamin D is high blood calcium (hypercalcemia), which causes nausea or vomiting, abdominal pain, thirst, frequent urination, confusion and weakness. In the large trial at 2,000 IU a day, no excess of hypercalcemia or other adverse events was identified. Risk rises with high doses, and with several sources added together.

What goes wrong when vitamin D is too high

A 2018 clinical review describes vitamin D toxicity as rare but serious. Its most noted symptoms are confusion, apathy, recurrent vomiting, abdominal pain, frequent urination, thirst and dehydration, and its clinical signature is severe hypercalcemia from excessive long-term intake. It is usually caused by inadvertent or improper intake of extremely high doses of concentrated preparations, and it is defined in the blood by 25-hydroxyvitamin D above about 150 ng/mL (375 nmol/L). The same review notes that some people are unusually sensitive: for them, doses considered safe for the general population can raise calcium.

What the trials found at and near our dose

• 2,000 IU a day, about 5 years. In VITAL (25,871 US adults aged 50 and over, vitamin D3 against placebo, median 5.3 years), no excess risk of hypercalcemia or other adverse events was identified. The fracture and depression analyses of the same trial also found no substantial adverse-event differences.
• 3,200 to 4,000 IU a day. A 2023 meta-analysis of 22 randomised trials (12,952 adults, all vitamin D3, six months or longer) found hypercalcemia more common than on control (relative risk 2.21, 95% CI 1.26 to 3.87), about 4 additional cases per 1,000 people. Falls (relative risk 1.25) and hospitalisation (1.16) were also higher. Kidney stones, high urinary calcium and deaths did not differ significantly. The authors flagged incomplete reporting of safety data, and concluded that this dose is "not completely safe".
• 4,000 and 10,000 IU a day, three years. A trial of 311 healthy adults aged 55 to 70 found lower radial bone density on 4,000 IU (2.4% change) and 10,000 IU (3.5%) than on 400 IU (1.2%). Whether this is harmful was not established.
• 400 IU with 1,000 mg calcium, seven years. In the Women's Health Initiative (36,282 postmenopausal women), the combination raised the risk of kidney stones (hazard ratio 1.17, 95% CI 1.02 to 1.34). That trial used calcium as well as vitamin D3, and our softgel contains no calcium, so it does not tell you what vitamin D alone does.

Can vitamin D3 make you sleepy or dizzy?

Sleepiness and dizziness are not outcomes any of the trials above reported for vitamin D, so we cannot say the vitamin causes them or does not. What the toxicity review does list is confusion and apathy, as part of high blood calcium. At doses well under the upper limit that is not expected, but if you feel unusually sleepy, dizzy or confused after starting, stop and ask a clinician. You will need a blood test to tell whether it is the vitamin.

Stacking is the usual route to too much

The upper limit is 100 mcg (4,000 IU) a day from food and supplements together. One of our softgels is 50 mcg (2,000 IU), half of it. Our Personal Routines "D Complex" pill carries 125 mcg (5,000 IU) of vitamin D3 on its own, over the limit, and the two together come to 175 mcg a day, 1.75 times the limit. Do not combine them, and count vitamin D in any multivitamin, fish-oil or calcium product too. The numbers are in how much vitamin D should you take a day.

What is in our softgel that could matter to you

Electric Tiger Vitamin D3 contains 50 mcg (2,000 IU) of vitamin D3 as cholecalciferol per softgel, and the other ingredients are gelatin, glycerin, water, soybean oil and corn oil. If you avoid soy, corn or animal-derived gelatin, check that line first: it is not vegan, and not suitable for strict vegetarians. Our warning says not to exceed the recommended dose, to count vitamin D from other supplements, and to ask a physician before use if you are pregnant or nursing or under 18. We give no dosing guidance for those groups.

Questions people ask

What are the side effects of taking vitamin D3?

At 2,000 IU a day, the large trial identified no excess of hypercalcemia or other adverse events. At higher intakes, hypercalcemia and its symptoms (nausea, vomiting, thirst, frequent urination, confusion) are the concern, and a small excess of hypercalcemia appeared at 3,200 to 4,000 IU.

What are the side effects of vitamin D3 and K2, or of cholecalciferol, or of a supplement generally?

Cholecalciferol is vitamin D3, so the above applies. We sell no K2 and cite no trial of the pair, so we cannot describe side effects of the combination.

Does 2,000 IU or 5,000 IU cause side effects?

2,000 IU: none identified in VITAL. 5,000 IU (125 mcg) is above the 100 mcg adult upper limit, and 3,200 to 4,000 IU already showed a small excess of hypercalcemia in pooled trials. Higher amounts are a clinician's decision.

Can vitamin D3 make you sleepy or dizzy?

See the section above: not reported as outcomes in the trials we cite. If it happens, stop and ask a clinician.

Can vitamin D3 upset your stomach or cause diarrhea?

Nausea and abdominal pain are listed as symptoms of vitamin D toxicity. Whether ordinary doses affect the stomach is covered in does vitamin D cause diarrhea.

Who should be more careful?

People with high blood calcium, a history of stones or other calcium-related conditions, and anyone on certain medicines: see who should not take vitamin D.