Vitamin supplement capsules

Should You Take Supplements? What the Science Actually Shows

10 December 20237 min read By Dushyanta Tomar

The global supplement market is worth around 180 billion US dollars in 2025 and growing. Most of that revenue covers products with little or no evidence in healthy adults. A small handful of supplements have strong, replicated trial evidence and are worth taking. The rest range from harmless waste of money to actively counterproductive.

This post ranks the most commonly used supplements into three evidence tiers, lists the doses backed by trials, and flags the categories where regulation is weakest and quality risk is highest.

5
Supplements with strong evidence in healthy adults
~10%
UK adults with low or deficient vitamin D status (NDNS)
10ug
UK NHS recommended daily vitamin D from October to March
3-5g
Daily creatine monohydrate dose with strongest evidence
Sources: NHS vitamin D guidance 2025. Kreider et al., ISSN creatine position stand 2017.

Tier 1: strong evidence, take if relevant

Five supplements have replicated trial evidence in healthy adults. Each has a clear use case, a defined dose range, and a safety profile that supports daily use.

Common supplements grouped by evidence quality Share of products in each evidence tier (qualitative) Strong evidence (~12%) Creatine, whey, caffeine, omega-3, D Moderate evidence (~25%) Magnesium, B12, iron, ashwagandha Weak or no evidence (~63%) Multivitamins, BCAAs, fat burners
Qualitative segmentation based on Examine.com evidence summaries and ISSN position stands. Percentages illustrative, not exact.

Creatine monohydrate. 3 to 5 grams per day. The most-studied performance supplement in history, with over 1,000 trials. Improves strength, lean mass, and high-intensity output. Emerging evidence for cognitive support in older adults and during sleep deprivation.

Whey or plant protein powder. 20 to 30 grams per serving as needed to hit daily protein targets (1.2 to 1.6 g per kg body weight). Not magical, but convenient. Useful when whole food protein is hard to fit into the day.

Caffeine. 3 to 6 mg per kg body weight, 30 to 60 minutes pre-training. The most evidence-backed ergogenic aid. Improves endurance performance, strength output, and reaction time. Cap intake at 400 mg per day total to avoid sleep disruption.

Omega-3 (EPA plus DHA). 1 to 2 grams per day from fish oil or algae oil. The 2019 AHA Science Advisory and the REDUCE-IT trial support omega-3 for triglyceride reduction and cardiovascular event reduction in selected populations. Useful if your weekly oily fish intake is low.

Vitamin D3. 10 micrograms (400 IU) daily from October to March in the UK per NHS guidance, with higher doses considered if a blood test shows deficiency. Vitamin D supports bone health and immune function. Routine supplementation in winter is recommended for the UK population.

Tier 2: moderate or situational evidence

This tier benefits specific groups (older adults, restricted diets, deficient populations) but is not routinely needed for the average adult eating a varied diet.

Magnesium. 200 to 400 mg per day if dietary intake is low. Useful for sleep onset, muscle cramps, and people on long-term proton-pump inhibitors. Magnesium glycinate and citrate absorb better than oxide.

Vitamin B12. 2.4 micrograms per day for general adults, higher for vegans, vegetarians, and people over 50 (absorption falls with age). Deficiency presents as fatigue, low mood, and tingling.

Iron. Only if a blood test confirms low ferritin or iron-deficiency anaemia. Higher prevalence in menstruating women, endurance athletes, and people with restricted diets. Excess iron is harmful, so do not supplement blind.

Beta-alanine. 3 to 6 grams per day in divided doses for athletes doing high-intensity efforts lasting 1 to 4 minutes (rowing intervals, CrossFit, sprint cycling). Limited use case outside of competitive sport.

Ashwagandha. 300 to 600 mg per day of standardised extract. The 2024 review of 12 RCTs in Journal of the American Nutrition Association found modest reductions in cortisol and anxiety scores. Effects are smaller than meditation, exercise, or sleep optimisation, but the supplement is cheap and well-tolerated.

Tier 3: weak or no evidence in healthy adults

The supplements driving most market revenue sit here. Each has been heavily marketed and most have failed to show benefit in randomised trials.

Multivitamins. The 2018 JAMA review of 18 trials covering 2 million participants found no reduction in cardiovascular events, cancer, or all-cause mortality from routine multivitamin use in well-nourished adults. Targeted single-nutrient supplements based on blood test results outperform shotgun multivitamins.

BCAAs (branched-chain amino acids). Marketed as muscle-builders. Multiple trials show BCAA supplementation does not enhance muscle protein synthesis above what total daily protein provides. If you hit your protein target, BCAAs add no measurable value.

Fat burners and thermogenics. The active ingredients (caffeine, green tea catechins, capsaicin) produce small effects in isolation. Proprietary blends rarely disclose doses, often contain banned stimulants, and have triggered FDA and MHRA recalls.

Detox and cleanse products. The liver and kidneys handle detoxification continuously. No supplement category meaningfully accelerates that process. Most "detox" products work via diuretics and laxatives, producing weight loss that is water and stool, not fat.

Most testosterone boosters. Fenugreek, tribulus, and "natural T boosters" do not produce clinically meaningful changes in testosterone in healthy adult men. Sleep, body composition, and resistance training have much larger effects.

Quality and regulation

The supplement industry is regulated more loosely than pharmaceuticals. In the UK and EU, supplements are regulated as foods, not medicines. Manufacturers are responsible for safety but do not need to prove efficacy. Independent product testing reveals consistent discrepancies between labelled and actual content.

Three quality markers worth checking before buying:

Third-party testing certification. Look for Informed Sport, Informed Choice, NSF Certified for Sport, or USP Verified. These programmes test products for label accuracy and banned substance contamination.

Single-ingredient products over proprietary blends. A bottle labelled "5g creatine monohydrate" is more transparent than a bottle labelled "Pre-workout matrix 8g" with no per-ingredient breakdown.

Established manufacturers. Larger UK and EU brands with long operating histories, GMP certification, and visible quality control programmes are lower risk than imported or unbranded products from online marketplaces.

Frequently asked questions

Should I take a multivitamin as insurance?
For most adults eating a varied UK diet, no. The 2018 JAMA review found no reduction in major health outcomes from routine multivitamin use. If you have a restricted diet, follow a specific protocol like keto or carnivore, or have malabsorption conditions, ask your GP for targeted blood tests and supplement specific deficiencies.
Is creatine safe for women and older adults?
Yes. The ISSN position stand reviewed safety data from 30-plus years of trials including women, adolescents (over 16), and older adults. No serious adverse effects at the standard 3 to 5 g per day dose. Older women benefit from creatine for bone density and muscle preservation alongside resistance training.
How do I know if I am vitamin D deficient?
A blood test (25-hydroxyvitamin D, or 25(OH)D) gives the answer. UK NHS labs and private services like Medichecks offer the test. Levels below 25 nmol/L indicate deficiency. Levels between 25 and 50 nmol/L indicate insufficiency. Optimal is 75 to 125 nmol/L for most adults.
Can supplements replace medication?
No. Supplements are for nutritional support, not for treating diagnosed conditions. Do not substitute supplements for prescribed medication. Always tell your GP and any specialist what you are taking, as supplements can interact with prescribed drugs (omega-3 with blood thinners, magnesium with certain heart medications, vitamin K with warfarin).
What about protein powder, is it really necessary?
Necessary, no. Convenient, yes. If you consistently hit your daily protein target (1.2 to 1.6 g per kg body weight) from whole food, protein powder adds nothing. If you struggle to hit the target, especially during reduced appetite phases (GLP-1 medication, illness, intense training), a scoop of whey or pea protein per day is the cheapest way to close the gap.
How do I check whether a specific supplement has evidence?
Examine.com publishes free evidence summaries for every common supplement, graded by study quality and effect size. PubMed direct searches work for primary research. Avoid supplement-brand websites and influencer pages as your sole source.

Bottom line

The honest supplement shortlist for most UK adults is short. Creatine if you lift. Protein powder if you struggle to hit your daily target. Caffeine if you train. Omega-3 if you do not eat oily fish regularly. Vitamin D in autumn and winter. Targeted single-nutrient supplements based on blood tests if deficient. Everything else is either situational or money for nothing. Spend the savings on better food, training, and sleep.

Get a personalised supplement plan
If you want a supplement protocol matched to your goals, blood test results, and training load (and the confidence you are not wasting money), book a nutrition consultation.
Visit www.dushyantatomar.com

Sources

  • Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017. PubMed
  • Jenkins DJA, et al. Supplemental Vitamins and Minerals for CVD Prevention and Treatment. Journal of the American College of Cardiology, 2018. PubMed
  • Skulas-Ray AC, et al. Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation, 2019. PubMed
  • Goldstein ER, et al. International society of sports nutrition position stand: caffeine and performance. Journal of the International Society of Sports Nutrition, 2010. PubMed
  • Jager R, et al. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 2017. PubMed
  • NHS. Vitamin D. NHS Vitamins and minerals. NHS
  • NHS. Multivitamins, minerals and supplements. NHS Eat Well. NHS
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