People take vitamin and mineral supplements to help them feel better. If you get a headache after taking vitamins, it's time to do a little sleuthing. The first thing you need to find out is which vitamins cause headaches and whether they're the cause of your discomfort. Mineral supplementation does not appear to cause headaches, but excessive amounts of vitamins A and C can.
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General Warnings for Supplements
Vitamin and mineral supplements can affect people differently. Each person taking the same supplement may experience different side effects — or none at all. As a general caution, health sites including Drugs.com report that all multivitamins could cause side effects, including upset stomach and headache. However, these effects are not considered serious unless they're accompanied by hives, difficulty in breathing or swelling of the face, lips, tongue or throat. These symptoms likely indicate an allergic reaction and require immediate medical attention.
Excess Vitamin A Side Effects
As a fat-soluble vitamin, extra vitamin A is stored in the body — unlike excesses of water-soluble vitamins, which are excreted in urine. Natural forms of the vitamin from food sources aren't likely to cause a problem, but large amounts of pre-formed vitamin A from supplements can cause headaches, along with dizziness, nausea, coma and death.
The daily value for vitamin A is 5,000 IU, and it's easy to get this amount from a daily diet rich in fruits, vegetables and protein. If you add a supplement, you may go over — or way over — the DV. The upper tolerable intake — the amount at which serious side effects may occur — is 10,000 IU. If you're taking a vitamin A supplement, check the label and speak with your doctor about whether excess vitamin A could be causing your headaches.
Read more: The 12 Most Overrated Supplements
Too Much Vitamin C
Taking megadoses of vitamin C is fairly common — especially during cold and flu season. Although vitamin C is a water-soluble vitamin and excess is excreted in urine, very large doses can result in unabsorbed vitamin in the intestinal tract. Possible side effects of this residual vitamin C include headache, along with nausea, diarrhea, stomach cramps and heartburn. The daily recommendation for vitamin C from food and supplements is 75 mg for women and 90 mg for men. Taking more than 2,000 mg per day — the upper tolerable limit — could lead to undesirable effects.
Interactions With Medications and Supplements
Another cause of your headache after taking vitamins could be interactions with medications you're taking or the effects of vitamin supplements on the absorption of other nutrients. For example, the National Institutes of Health reports that very large amounts of vitamin C can inhibit the absorption of vitamin B12. According to the National Headache Institute, B vitamins, including B12, lower the amount of the amino acid homocysteine, high levels of which can lead to headaches.
Low levels of vitamin D can also cause headaches. Certain medications, including carbamazepine, phenytoin, primidone, barbiturates and some HIV treatments can interfere with vitamin D, potentially leading to a deficiency. The best thing to do is make an appointment with your doctor to go over any supplements you're taking and any medications you're on to determine whether an interaction could be at the root of your problem.