Compared with recent calcium intake recommendations, most people have calcium-deficient diets, and less than 10% of women in the U.S. have adequate dietary intakes.97 Good calcium nutrition throughout life is essential for achieving peak bone mass and preventing deficiency-related bone loss.98 Calcium supplements are effective in increasing bone mass in children99 100 101 and slowing bone loss in adults according to most,102 103 104 105 106 107 though not all,108 double-blind studies. Calcium supplements have also been shown to reduce the risk of bone fractures in some elderly adults.109 110 111 112 The protective effect of calcium on bone is one of very few health claims permitted by the FDA. In order to achieve the 1,500 mg per day calcium intake deemed optimal by many researchers for postmenopausal women, 800 to 1,000 mg of supplemental calcium are generally added to diets that commonly contain between 500 and 700 mg of calcium per day.
Phosphorus is a necessary nutrient, but diets are almost always adequate in this mineral.113 Some authorities have suggested that excess intake of phosphorus is hazardous to normal calcium and bone metabolism.114 However, this idea has been challanged.115 In any case, for most people there does not seem to be a need for phosphorus supplementation. For this reason, many multivitamin-mineral supplements do not contain phosphorus. The only exception is for elderly people, whose diets tend to be lower in phosphorus. Calcium interferes with phosphorus absorption, so older people who are taking a calcium supplement might benefit from taking additional phosphorus.116
Dietary magnesium deficiency may occur in up to 25% of adult women in the U.S. and in even higher numbers of elderly people of both sexes.117 Magnesium supplements of at least 250 mg per day may help prevent bone loss.118 119
While potassium is lower in modern diets compared with so-called primitive diets, true deficiencies are uncommon.120 Some,121 though not all,122 research suggests that raising potassium intake may help prevent high blood pressure. Other research suggests higher potassium intake may help prevent stroke.123 However, the maximum amount of supplemental potassium allowed in one pill (99 mg) is far below the recommended amounts (at least 2,400 mg per day). Multiple potassium pills should not be taken in an attempt to get a higher amount, since they can irritate the stomach. The best way to get extra potassium is to eat several servings per day of fruits, vegetables, or their juices.
Iron deficiency is not uncommon among some groups of healthy people, including some vegetarians,124 menstruating girls and women,125 pregnant women,126 and female and adolescent athletes.127 Nonetheless, many people in these groups are not iron deficient 128 and excessive iron intake has been associated in some studies with heart disease,129 some cancers,130 diabetes,131 increased risk of infection,132 and exacerbation of rheumatoid arthritis.133 While none of these links has yet been proven, people should avoid iron supplements unless they have been diagnosed with having, or being at high risk of, iron deficiency.
Iodine deficiency is a concern in many developing countries,134 Until recently it was considered abundant in Western diets, due to the introduction of iodized salt and the iodine added to many foods.135 However, iodine intake has decreased considerably in recent years and may be low in as many as 12% of the total U.S. population, and 15% of women of childbearing age.136 These numbers may be greater in countries where iodized salt is not available. Still, most people have adequate iodine intake unless they avoid iodized salt, seafood, and sea vegetables. People with thyroid diseases should check with their doctor before using iodine supplements.
Zinc deficiency is not common in Western countries, except in people with low incomes.137 138 Zinc supplements (10 mg per day) have prevented growth impairment in deficient American and Canadian children.139 Supplementation with 25 to 150 mg of zinc per day has been shown to increase immune function in healthy people.140 141 142 143 However, too much zinc has been reported to impair immune function and some healthcare practitioners recommend no more than 30 to 50 mg per day.144 It is unknown whether these immune system changes are sufficient to cause or prevent infections or other diseases in people taking zinc supplements. Regular supplementation with zinc should be accompanied by copper supplements to prevent zinc-induced copper deficiency.
The average dietary copper intake in the U.S. has been found to be below accepted standards.145 However, the significance of this is unclear, since symptomatic copper deficiency is quite rare.146 Supplementation with 3 mg per day of copper may help prevent bone loss.147 Since zinc can interfere with copper absorption, copper should be taken whenever zinc supplements are taken for more than a few weeks.148
Dietary intake of manganese is adequate for most people, according to recent studies in the U.S.149 However, manganese, along with other trace minerals, is often low in refined and processed foods.150 151 People whose diets consist primarily of these types of foods may have low manganese intake. Manganese deficiency has been associated with osteoporosis in an unpublished study.152 A double-blind trial found that a combination of mineral supplements including manganese prevented bone loss in postmenopausal women.153 No other studies have investigated the health effects of manganese supplementation. Manganese may be especially important to include when iron is supplemented, since iron can reduce manganese absorption and cause lower body levels of manganese.154
Chromium nutrition has been difficult to study because of technical problems in analyzing foods and human body fluids for chromium content. Partly for this reason, there is disagreement about the extent of chromium deficiency in Western societies. Many studies have found sub-optimal levels of chromium in the diet, compared to published recommendations.155 156 157 However, some authorities question the validity of the recommended minimum requirements.158 Chromium deficiency has been associated with blood sugar and cholesterol abnormalities.159 Also, chromium levels in the body decline as people get older, which is when these problems often appear.160 Therefore, while chromium supplements have not been tested for their ability to prevent diabetes or heart disease, many healthcare practitioners recommend chromium supplements as a reasonable precaution. A few single case reports have described possible serious side effects in people taking large amounts of chromium, from 600 to 2400 mcg per day, 161 162 163 although it is not clear whether chromium was responsible for these reactions.
Dietary intake of selenium appears to be adequate in most people. This is according to recent studies in the U.S. based on the Recommended Dietary Allowance of 70 mcg per day of selenium.164 However, a double-blind study found that people given a supplement of 200 mcg of yeast-based selenium per day for 4.5 years had a 50% drop in the cancer death rate over seven years compared with the placebo group.165 Higher amounts of selenium than are available in the diet may be necessary for this protective effect. The upper end of safe long-term selenium intake has been estimated to be 350 to 400 mcg per day.166
Molybdenum is an essential trace element with low potential for toxicity.167 Since little is known about human needs and deficiencies are quite rare, estimated requirements are based on what people typically receive in their diets.168 Cancer and cardiovascular disease prevention studies in China found no benefit from a supplement containing molybdenum and vitamin C.169 170 No other research has investigated disease prevention with molybdenum supplements.