The term "metabolism" refers to the chemical reactions that take place in your body each day, and the energy -- in the form of calories -- that's burned carrying out those reactions. Part of your metabolic rate depends on your genetics; if you're predisposed to a slow metabolism, for example, you'll gain weight more easily than someone with a naturally fast metabolism. Most vitamin supplements won't significantly boost your metabolism if you're already healthy. However, some supplements might offer slight benefits, and others might restore your metabolism if you're currently suffering from a deficiency. Never take supplements without first talking to your doctor, though, or you risk side effects.
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Vitamin D and Calcium
Vitamin D and the mineral calcium might have a slight beneficial effect on your metabolism, though they likely won't take you from a slow metabolism to a fast one. However, vitamin D and calcium can slightly boost your calorie burn throughout the day and might help you lose body fat, according to a literature review paper published in Obesity Reviews in 2012, though the review authors caution that more research is needed to know how well they really work.
Taking calcium and vitamin D offers other benefits, too; both nutrients benefit the health of your bones, and calcium also plays a key role in muscle function. However, vitamin D is a fat-soluble vitamin that can accumulate in your body if you take too much, so you should never take more than the dosage recommended by your doctor.
Zinc and Selenium, Thyroid Hormones and Metabolism
Multivitamin supplements containing zinc and selenium might offer a slightly metabolism boost in some cases. Both minerals play a role in thyroid function; selenium helps control the levels of active thyroid hormone in your system, while zinc makes up a component of cellular proteins, called enzymes, that let your cells respond to thyroid hormone. A shortage of either mineral could affect thyroid hormone function, and, since your thyroid hormones affect your metabolism, low selenium or zinc levels might affect your metabolic rate.
That doesn't mean you should take zinc or selenium to boost thyroid function without first checking with your doctor, though. Thyroid hormone imbalances require medical attention, and accidentally taking too much zinc or selenium can cause side effects. Selenium, for example, could cause nerve damage in some cases.
Taking B-complex vitamins won't necessarily make you burn more calories throughout the day if you're healthy, but they can provide metabolic support. Your cells use specialized proteins, called enzymes, to convert the nutrients in food to energy, and several B-complex vitamins help activate these enzymes, so can properly turn the food you eat into useable fuel for your active lifestyle. B-complex vitamins also help you make red blood cells, which supply your cells and tissues -- including your muscles -- with fresh oxygen.
If you're currently feeling fatigued due to a deficiency in one or more B-complex vitamins, taking supplements can correct the deficiency and boost your energy levels, so you can get more activity and burn more calories throughout the day. However, if you're not suffering from a deficiency, taking supplements might not offer any benefit.
Vitamins With Metabolism-Boosting Herbs
If you're taking a multivitamin that contains an herbal blend in addition to essential vitamins and minerals, you might get a slight metabolism-boosting benefit. Green tea extract -- a common ingredient in "weight loss" multivitamins -- contains caffeine and a chemical called EGCG, which might work together to slightly increase your calorie burn, reports a review article published in Chinese Medicine in 2010. However, it's not clear how much herbal blends really help, and supplement manufacturers don't have to prove that their products contain the active herbal ingredients listed on the label or show that their supplements significantly increase weight loss. If you're interested in herbal vitamins, talk to your doctor about the best ones to take, and stick to the dosage she recommends.