Persistent itching can be maddening, especially when you can’t identify the cause. If you haven’t switched to a new laundry detergent or soap lately, and if you have no other symptoms, you might consider that what you’re ingesting is the source of the problem. Food allergies can cause itching, but some supplements can do so as well, particularly when taken in excess or in combination with certain foods or beverages.
Sunlight prompts your body to make vitamin D on its own, but not everyone gets enough this way. If your complexion is dark, or if you live in a climate that's prone to cloudy, cold days, you might worry that you suffer from a deficiency and take supplements to bolster your body’s resources. Although you can’t get too much vitamin D from the sun, and it’s unlikely that you’ll ingest too much from food sources, if you combine foods high in vitamin D with excessive supplements, you might get too much, and itching can result. Foods high in vitamin D include fatty fish and fortified cereals and milk. Vitamin D supplement doses range from about 800 IU in multivitamins to as much as 1,000 IU in individual supplement form. According to the University of Maryland Medical Center website, the recommended daily allowance for adults is 600 IU. If you combine a 1,000 IU vitamin D dose with other dietary sources, you can conceivably ingest too much, and you might find yourself itching.
High doses of vitamin A might also be the culprit behind your itching. According to the Colorado State University Extension website, most American adults run no risk of being deficient in this vitamin, even without taking supplements. Many individuals take supplements, anyway. Some multivitamins include vitamin A in the form of beta-carotene, which won’t cause an itching reaction. However, if your supplement doesn't specifically say how much, if any, of the vitamin A content is from beta-carotene, you might find yourself scratching, especially if you take upwards of 3,000 mcg over the course of a day. Some multivitamins contain a great deal of vitamin A, so if you additionally take another vitamin A supplement, you could reach this level.
Niacin, or vitamin B3, is somewhat notorious for causing adverse physical reactions in high doses. It's surprisingly easy to ingest too much of it without being aware. For example, energy drinks usually have a very high niacin content. If you use these drinks, and if you also take a multivitamin supplement that includes niacin, you can easily get too much. Your body doesn’t need more than 17 mg a day, and some multivitamins include as much as 14 mg. Even one energy drink a day, in addition to a multivitamin, can put you well over 17 mg, and itchy skin can result.
Magnesium is an element found in many multivitamins, usually in doses of about 50 mg. Some laxatives and antacids also include it as magnesium oxide, because this form is relatively inexpensive to manufacture. You can also purchase magnesium as a single supplement without a prescription. If you double-up on sources, you might get too much. Itchiness can result, usually accompanied by a rash or hives. If this occurs, seek medical help, particularly if you also experience light-headedness, nausea or weakness. Take your antacid, laxative or vitamin supplements with you to show your physician exactly how much magnesium you’ve ingested.