Are dietary supplements sold by Costco (Costco Wholesale Corporation) effective?

From the Guidelines

Dietary supplements sold by Costco are not effective for the primary prevention of cardiovascular disease and cancer in healthy adults without special nutritional needs. The U.S. Preventive Services Task Force recommendation statement published in the Annals of Internal Medicine in 2014 1 found that vitamin, mineral, and multivitamin supplements have few known benefits and may have potential harms, such as adverse effects caused by excessive doses of vitamins. Some key points to consider when evaluating the effectiveness of dietary supplements include:

• Potential preventable burden: evidence from in vitro and animal research and population-based epidemiologic studies supports the hypothesis that oxidative stress may play a fundamental role in the initiation and progression of cancer and common cardiovascular diseases 1
• Potential harms: important harms have been shown with β-carotene in persons who smoke tobacco or have an occupational exposure to asbestos, and excessive doses of vitamins can cause adverse effects 1
• Quality control: the content and concentration of ingredients in commercially available formulations probably vary considerably, making extrapolating results obtained from controlled clinical trials challenging 1 While Costco's Kirkland Signature supplements undergo third-party testing for quality and purity, meeting FDA regulations for dietary supplements, the effectiveness of any supplement depends on individual health needs, existing deficiencies, and how the body absorbs nutrients. It is essential to consult with a healthcare provider to determine which supplements and dosages are appropriate for specific health needs, as individual requirements vary based on age, gender, health conditions, and medications. In general, a balanced diet is the best way to ensure adequate nutrition, and supplements should be used to complement, not replace, a healthy diet.

From the Research

Effectiveness of Dietary Supplements

• The effectiveness of dietary supplements sold by Costco or any other retailer is unclear, as the evidence supporting their use is limited 2, 3, 4, 5, 6.
• Some supplements, such as nitrate, caffeine, creatine, protein, and polyunsaturated fatty acids, have shown beneficial effects on muscle strength and mass, but the evidence is not consistent for all supplements 2.
• Vitamins and minerals, such as vitamin D and folic acid, may be beneficial for specific populations, but the evidence for their use in preventing chronic diseases is limited 3, 6.
• Certain supplements, like plant sterols/stanols, omega-3 fatty acids, and niacin, have strong scientific evidence supporting their health benefits, while others, such as garlic and antioxidants, lack evidence 4.

Safety and Regulation

• Dietary supplements are not closely regulated, and their safety and efficacy are not always ensured 4.
• Some supplements, such as those containing metabolic stimulants like caffeine and ephedra, may produce adverse side effects and should be avoided 5.
• The safety of many frequently used supplements is unknown, and excessive consumption of certain vitamins and minerals can have detrimental health effects 2, 3.

Specific Supplements

• Weight-loss supplements have limited evidence supporting their effectiveness, and many have no or few randomized clinical trials examining their efficacy 5.
• Some foods or supplements, such as green tea, fiber, and calcium supplements or dairy products, may complement a healthy lifestyle to produce small weight losses or prevent weight gain over time 5.
• Daily low-dose multivitamin supplementation has been linked to reductions in the incidence of cancer and cataracts, especially among men 6.