As the US nutritional and dietary supplements market remains robust — an estimated $41.1 billion in sales in 2016 — the Academy of Nutrition and Dietetics is cautioning against the routine and indiscriminate use of these dietary add-ons.
In an updated position paper, published online November 20 in the Journal of the Academy of Nutrition and Dietetics, the academy states that while single- and multiple-vitamin and mineral supplements may benefit the many Americans whose diets are lacking in micronutrients, there is no scientific evidence to warrant their regular use for preventing chronic disease in healthy individuals.
This conclusion is based on evidence reviews by a number of bodies, including the National Institutes of Health, the Agency for Healthcare Research and Quality (AHRQ), and the US Preventive Services Task Force (USPSTF).
“Those with increased requirements secondary to growth, chronic disease, medication use, malabsorption, pregnancy and lactation, and aging may be at particular risk for inadequate dietary intakes,” write Melissa Ventura Marra, PhD, an assistant professor of human nutrition and foods at West Virginia University in Morgantown, West Virginia, and Regan Bailey, PhD, MPH, an associate professor of nutrition science at Purdue University in West Lafayette, Indiana.
About a third of US adults use a multivitamin-mineral supplement, the authors note. Prudently used, supplements may help close gaps in deficient diets; a previous analysis of data from the National Health and Nutrition Examination Survey show 25% to 70% Americans have low dietary intake of calcium, magnesium, and vitamins A, C, D, and E.
Micronutrient supplements may specifically benefit women intending to conceive or already pregnant, babies primarily breast-fed, alcohol-dependent individuals, and those with age-related macular degeneration, according to the AHRQ statement.
Haphazard use of supplements, however, may raise consumption of certain micronutrients above the tolerable upper intake levels (ULs), thereby posing health risks such as adverse interactions with medications and inhibition of other essential micronutrients. Although most adult users do not exceed ULs, the authors warn some may unwittingly consume excessive amounts of iron (9%), zinc (9%), folic acid (7%), calcium (6%), magnesium (6%), vitamin B6 (3.5%), vitamin A (3%), and vitamin C (1.6%).
“Consumers may not be well informed about the safety and use of these products, and some may have difficulty interpreting product labels,” the authors write.
They stress that care providers offering nutritional advice should keep up to date on the efficacy and safety of these products, as well as on regulatory issues about their use. The paper gives a comprehensive list of authoritative resources for potential contraindications and drug and food interactions, including the AHRQ, the Cochrane Collaboration, the US Food and Drug Administration, the Office of Dietary Supplements, and the National Academy of Medicine.
The position paper supports the following recommendations on specific micronutrient supplements:
400 IU/day vitamin D for mainly breast-fed infants
400 to 800 µg/day folic acid (if not consumed in fortified foods) for women planning pregnancy
antioxidant supplements for those with intermediate or advanced age-related macular degeneration
2.4 mg/day vitamin B12 from supplements or fortified foods for those age 50 and older
The authors also provide specific caveats on the use of supplements:
Iron supplements should be avoided by postmenopausal women and men and individuals homozygous for hemochromatosis.
Postmenopausal women should avoid retinol supplements, which have been linked to reduced bone mineral density and increased hip fracture risk.
High supplemental intakes of vitamin B6 have been tied to sensory neuropathy.
High-dose iron pills can decrease zinc absorption, while zinc can impede copper absorption. Calcium supplements inhibit both heme and nonheme iron absorption.
High-doses can adversely affect medications; for instance, vitamins E and K can interfere with anticoagulants such as Coumadin.
High-dose beta-carotene may raise lung cancer risk in smokers.
The USPSTF found insufficient evidence to support commonly prescribed calcium and vitamin D supplements for reducing fracture risk in postmenopausal women and suggested these may boost kidney stone risk.
For patients who want to take supplements, Ventura Marra said that a one-a-day multivitamin and mineral supplement that provides close to 100% of the recommended daily value for most nutrients can help prevent inadequacies and is generally safe for healthy individuals. “Ironically, most patients taking a multivitamin supplement aren’t the ones who generally need them most,” she told Medscape Medical News.
By contrast, consuming single vitamins and minerals is generally not advisable unless a specific nutrient deficiency is being treated, Ventura Marra continued.
“When making recommendations to patients, we need to consider individual factors like the overall quality of the diet, health conditions, and medication use,” she said. “Patients following low-calorie diets, who limit certain foods, or have health conditions that interfere with nutrient absorption or use may especially benefit from micronutrient supplementation.”
She stresses that supplementation should not be viewed as a replacement for a healthy diet. “There are many nutrients like dietary fiber or phytochemicals that benefit health that they don’t provide,” she said. Instead, she recommends prescribing the addition of more nutrient-rich foods to patients’ diets to help meet shortfalls.
This position paper received no funding support. Bailey has been a scientific consultant to the National Institutes of Health, Office of Dietary Supplements, and has reported travel support from the Council of Responsible Nutrition. Ventura Marra has disclosed no relevant financial relationships.