The major minerals are needed in larger amounts as compared to the trace minerals. They're necessary for a variety of body functions. Taking major minerals as dietary supplements can have both benefits and risks, especially when used in large amounts.
The Institutes of Medicine, which is part of the National Academies, determines how much of each nutrient you need every day, as well the tolerable upper intake level (UL), which is the largest intake of each nutrient known to be safe. You typically don't have to worry about going over the ULs, unless you're taking large doses of dietary supplements -- it's difficult to go over the ULs from food sources alone.
Here's a look at the UL for each major mineral.
Calcium is necessary for strong bones and teeth, normal blood clotting, and nerve and muscle function. The recommended daily allowance is 1,000 to 1,200 milligrams for adults. The UL is 2,500 milligrams per day. Regularly consuming more than this amount may result in a higher risk of forming kidney stones and having kidney problems. Too much calcium may also cause hypercalcemia (blood levels of calcium that are too high). Milk alkali syndrome can occur after taking large amounts of calcium, usually in the form of calcium carbonate-based antiacids.
Chloride helps keep your body fluids in balance. The Institutes of Health has determined an adequate intake (AI) as 2.3 grams per day for most adults, with a little less as you age. The UL is 3.6 grams per day. Going over this amount on a daily basis may increase blood pressure when it's combined with sodium (salt is half sodium and half chloride).
Magnesium is needed for chemical reactions to occur in your body. The recommended daily allowance is 400 to 420 milligrams per day for men, and 310 to 320 milligrams per day for women. The UL is 350 milligrams per day, but unlike other minerals, only includes supplemental and pharmaceutical intake, but not from food sources. Consuming more than the UL every day could cause diarrhea.
PhosphorusPhosphorus is necessary for normal cell membranes, bone growth and for energy production. The recommended daily allowance is 700 milligrams per day, and the UL is 4,000 milligrams per day for most adults, and 3,000 milligrams per day for adults over the age of 70. Regularly consuming more than this amount can damage your bones and make it more difficult to absorb calcium from foods.
Potassium is necessary for normal fluid balance. The adequate intake is set at 4.7 grams per day. The Institutes of Medicine has not set a UL for this mineral, however taking large amounts of potassium supplements can cause hyperkalemia, which is too much potassium in the blood, and can be very dangerous.
Sodium is necessary for fluid balance. The adequate intake ranges for 1.2 grams to 1.5 grams per day for adults. The UL is 2.3 grams per day, and is easy to reach when you consume a diet high in processed foods. Regularly consuming more than this amount may increase blood pressure.
Taking Dietary Supplements
Most multi-vitamin/multi-minerals supplements are designed to help you reach your daily recommended intake for several nutrients, so they usually contain levels of vitamins and minerals that are well below the ULs. Some individual mineral supplements, and even some formulations, contain large amounts of minerals and you could reach the ULs if you take large doses.
Dietary supplements aren't well regulated so choose high quality supplements (I've got more tips for safe use of dietary supplements). To avoid reaching the UL for any nutrient, follow the directions on the dietary supplement label and don't take more than the recommended amount without speaking to your health care provider first.
Institutes of Medicine of the Institutes of Health. "Dietary Reference Intakes - Elements." Accessed December 25, 2012. http://www.iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Electrolytes_Water.pdf.
Institutes of Medicine of the Institutes of Health. "Dietary Reference Intakes - Electrolytes." Accessed December 25, 2012. http://www.iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Electrolytes_Water.pdf.