The supplement industry generates over $50 billion annually in the US alone and operates with significantly less regulatory oversight than pharmaceuticals. Products can make implied health claims, display impressive-sounding study references on their packaging, and price themselves as premium health interventions with essentially no requirement to demonstrate effectiveness comparable to what pharmaceutical products require.
This doesn’t mean supplements are uniformly useless. Some are well-supported by genuine evidence and address genuine nutritional gaps. The distinction between these and the majority of the market is the most useful information I can give you.
Vitamin D is produced by the skin in response to direct UV-B light exposure. In northern latitudes (above approximately 35°N, which includes most of the UK, northern Europe, Canada, and the northern US), UV-B light during the winter months (October through March in the UK) is insufficient in intensity to produce adequate vitamin D regardless of how much time you spend outdoors. The UK’s NHS recommends vitamin D supplementation for everyone during autumn and winter for this reason.
The dose supported by evidence for most adults is 1,000-2,000 IU (25-50 mcg) per day. Higher doses require a blood test to confirm deficiency before supplementing, as vitamin D toxicity is possible (though rare) at very high supplemental doses over extended periods. The blood test for 25(OH)D is widely available and worth getting once to understand your baseline.
Vitamin D3 (cholecalciferol) is the form that raises blood levels more effectively than D2 (ergocalciferol). Taken with a meal containing fat for optimal absorption.
Magnesium is involved in over 300 enzymatic processes including protein synthesis, muscle function, blood glucose control, and blood pressure regulation. The USDA dietary surveys consistently show that a significant percentage of the US adult population doesn’t reach the recommended daily intake through diet alone.
Symptoms of insufficient magnesium intake include muscle cramps, poor sleep quality, fatigue, and irritability — symptoms common enough in general populations that they’re rarely attributed to magnesium specifically, but that sometimes improve with supplementation.
The form matters: magnesium glycinate and magnesium malate are the forms with the best absorption and tolerability. Magnesium oxide is the cheapest and most commonly sold form and also the least bioavailable and most likely to cause digestive upset. The extra cost of glycinate or malate forms is worth it.
Creatine monohydrate has more peer-reviewed evidence supporting its effectiveness than any other supplement in the sports and fitness category. The evidence is specifically for strength and power output in exercise, lean body mass maintenance, and increasingly, cognitive function particularly in older adults and vegetarians (who have lower baseline creatine stores).
The dose is simple: 3-5g of creatine monohydrate per day, consistently, without loading phases. The “loading phase” (higher doses for the first week) produces faster saturation of muscle creatine stores but produces the same outcome over a longer timeline at the maintenance dose. There’s no meaningful long-term benefit to loading.
The form is simple: creatine monohydrate is the most studied, most effective, and least expensive form. The “advanced” forms — creatine HCl, creatine ethyl ester, buffered creatine — cost more, have less supporting evidence, and produce no meaningful superiority in outcome. Creatine monohydrate from any reputable manufacturer (Examine.com and Labdoor provide third-party testing verification) is the correct purchase.
Multivitamins for healthy adults eating varied diets: evidence for benefit in this population is weak. Specific deficiencies are better addressed with specific supplements once identified through testing rather than covered broadly with a multivitamin where most components pass through unused.
Detox supplements, cleanses, and liver support products: the liver and kidneys are the body’s detox system and they work continuously without supplemental support in people without organ disease. These products address a physiological process that is already happening efficiently.
Most weight loss supplements: the mechanisms claimed are either unproven, marginal in effect size, or both. No supplement currently available produces meaningful weight loss without dietary changes.
Collagen supplements: the amino acids in collagen supplements are absorbed in the gut and used by the body as amino acids generally — there’s no evidence that consuming collagen peptides preferentially routes them to skin collagen production rather than to general protein metabolism. The evidence for skin benefit specifically remains limited.