Which Supplements Actually Work? A Science-Based Guide

The supplement industry problem

The global dietary supplement market is worth over $150 billion annually, yet much of what's sold has little evidence behind it. Marketing claims often far exceed what research supports, and regulation is minimal compared to pharmaceuticals.

This guide cuts through the noise. We'll examine popular supplements based on scientific evidence, not marketing claims or anecdotes, helping you spend your money where it actually matters.

The tier system

We've categorised supplements into four tiers based on the strength and quality of evidence:

• Tier 1 - Strong evidence: Well-researched, proven effective for specific purposes
• Tier 2 - Moderate evidence: Promising research, may benefit some people
• Tier 3 - Limited evidence: Some positive studies, but more research needed
• Tier 4 - Weak/no evidence: Not recommended, save your money

Tier 1: Strong evidence

Creatine monohydrate

What it does: Increases phosphocreatine stores in muscles, improving high-intensity exercise performance and supporting muscle growth.

The evidence: Creatine is one of the most researched supplements in existence. Hundreds of studies demonstrate its safety and effectiveness for:

• Increasing strength and power output (5-10% improvement)
• Enhancing muscle growth when combined with resistance training
• Improving high-intensity exercise performance
• Potential cognitive benefits, especially under stress or sleep deprivation

Who benefits: Anyone doing resistance training or high-intensity exercise. Particularly effective for vegetarians/vegans who have lower baseline creatine stores.

Dosing: 3-5g daily of creatine monohydrate. Loading phases (20g/day for 5-7 days) work but aren't necessary - you'll reach saturation within a few weeks either way.

Safety: Extensively studied and safe for healthy adults. The only common side effect is modest water retention (1-2kg) within muscle tissue.

Verdict: Strongly recommended for anyone serious about strength or muscle building. Cheap, safe, and proven effective.

Protein supplements

What they do: Provide a convenient source of high-quality protein to help meet daily targets.

The evidence: Protein powder isn't magic - it's just food in powdered form. That said, a 2018 meta-analysis confirmed that protein supplementation combined with resistance training increases muscle mass and strength, particularly when baseline protein intake is insufficient.

Who benefits: Those struggling to meet protein targets through whole foods alone, people with busy lifestyles, or those needing post-workout convenience.

Types and differences:

• Whey protein: Fast-absorbing, high in leucine, excellent for post-workout
• Casein protein: Slow-absorbing, good before bed or as a meal replacement
• Plant proteins (pea, rice, soy): Good options for vegans; choose blends for complete amino acid profiles

Dosing: Whatever helps you hit your daily protein target. Use our protein calculator to determine your needs.

Safety: Very safe for healthy individuals.

Verdict: Recommended if needed to meet protein targets. Whole foods should be prioritised, but protein powder is a convenient, cost-effective option.

Caffeine

What it does: Stimulates the central nervous system, reducing perceived effort and enhancing performance.

The evidence: Caffeine is proven to improve:

• Endurance performance (2-4% improvement)
• Strength and power output (3-5% improvement)
• Reaction time and cognitive function
• Fat oxidation during exercise

Who benefits: Most exercisers, particularly for endurance or training when fatigued.

Dosing: 3-6mg per kg bodyweight, consumed 30-60 minutes before exercise. For a 70kg person, that's 210-420mg (roughly 2-4 cups of coffee).

Safety: Safe at moderate doses for healthy adults. Avoid late in the day to protect sleep. Those with anxiety, heart conditions, or caffeine sensitivity should be cautious.

Verdict: Effective and inexpensive. You don't need fancy pre-workouts - coffee works.

Vitamin D

What it does: Regulates calcium absorption, immune function, and muscle function.

The evidence: Vitamin D deficiency is extremely common, especially in northern latitudes, winter months, and people who work indoors. Low vitamin D is associated with:

• Reduced muscle strength and function
• Impaired immune function
• Increased injury risk
• Poor bone health

Supplementation in deficient individuals improves these outcomes. For those with adequate levels, additional supplementation shows limited benefits.

Who benefits: Anyone not getting regular sun exposure (most office workers, anyone in the UK during winter, people with darker skin).

Dosing: 1,000-4,000 IU daily for most people. Ideally, test your blood levels and adjust accordingly.

Safety: Safe at recommended doses. Very high doses (above 10,000 IU daily) for extended periods can cause toxicity.

Verdict: Recommended for most people in northern climates or those with limited sun exposure. Get tested if possible.

Tier 2: Moderate evidence

Omega-3 fatty acids (Fish oil)

What it does: Provides EPA and DHA, essential fatty acids with anti-inflammatory properties.

The evidence: Research suggests benefits for:

• Heart health (particularly in those with existing cardiovascular risk)
• Reducing inflammation
• Brain health and mood
• Potentially reducing muscle soreness after exercise

The evidence is strongest for cardiovascular benefits in at-risk populations. For general health in people already eating fatty fish regularly, benefits are less clear.

Who benefits: Those who don't eat fatty fish at least twice weekly, people with inflammatory conditions, and possibly those with depression.

Dosing: 1-3g combined EPA/DHA daily.

Safety: Very safe. High doses may increase bleeding risk in those on blood thinners.

Verdict: Recommended if you don't eat fish. If you eat salmon, mackerel, or sardines regularly, you may not need it.

Beta-alanine

What it does: Increases muscle carnosine levels, buffering acid buildup during high-intensity exercise.

The evidence: Shown to improve performance in activities lasting 1-4 minutes, such as:

• High-rep resistance training
• HIIT and interval training
• Rowing, cycling sprints, and similar efforts

Less effective for very short or very long duration activities.

Who benefits: Athletes doing high-intensity interval training or high-rep strength work.

Dosing: 3-6g daily, split into smaller doses to minimise tingling sensation (paresthesia).

Safety: Safe. The tingling is harmless and diminishes with smaller doses.

Verdict: Potentially useful for specific training styles. Not essential but may provide a small edge.

Magnesium

What it does: Involved in hundreds of enzymatic processes including muscle contraction, energy production, and sleep regulation.

The evidence: Many people don't meet dietary magnesium requirements. Supplementation in deficient individuals may improve:

• Sleep quality
• Muscle cramps
• Exercise performance
• Stress and anxiety

For those with adequate intake, additional supplementation shows minimal benefits.

Who benefits: Those with poor dietary intake, high stress, heavy exercise, or sleep issues.

Dosing: 200-400mg daily, preferably glycinate or citrate forms for better absorption.

Safety: Safe at recommended doses. High doses can cause digestive issues.

Verdict: Consider testing or try supplementing if you suspect deficiency.

Tier 3: Limited evidence

Ashwagandha

What it does: An adaptogenic herb claimed to reduce stress and improve various health markers.

The evidence: Some studies suggest benefits for:

• Reducing cortisol and perceived stress
• Modestly improving strength and recovery
• Supporting testosterone levels (though effects are small)

However, study quality varies, and many trials have methodological issues.

Who benefits: Possibly those under high stress or seeking modest performance improvements.

Dosing: 300-600mg daily of root extract (standardised to withanolides).

Safety: Generally safe for short-term use. Long-term safety data is limited.

Verdict: May be worth trying if stress management is a priority, but don't expect dramatic results.

Citrulline

What it does: Converts to arginine and increases nitric oxide production, potentially improving blood flow.

The evidence: Some studies show modest improvements in:

• High-rep resistance training performance
• Endurance exercise
• Muscle soreness recovery

Results are inconsistent, and effect sizes are generally small.

Who benefits: Possibly those focused on muscle pump or high-rep training.

Dosing: 6-8g citrulline malate (or 3-4g pure L-citrulline) pre-workout.

Safety: Safe.

Verdict: Optional for those who enjoy the pump sensation, but unlikely to make a significant difference.

Tier 4: Save your money

BCAAs (Branched-Chain Amino Acids)

The claim: Essential for muscle building and preventing muscle breakdown.

The reality: BCAAs are already present in any quality protein source. If you're eating adequate protein, BCAA supplements provide no additional benefit. A 2017 meta-analysis found no advantage of BCAAs over whole protein or adequate dietary protein.

The exception: May be useful for fasted training if you truly can't have any food beforehand, but even then, EAAs (essential amino acids) are a better choice.

Verdict: Not recommended for most people. Spend the money on regular protein instead.

Testosterone boosters

The claim: Dramatically increase testosterone and muscle growth naturally.

The reality: Most testosterone boosters contain ingredients with minimal to no effect on testosterone in healthy young adults. Ingredients like tribulus terrestris, fenugreek, and D-aspartic acid have failed to show significant testosterone increases in well-controlled studies.

Some ingredients may offer marginal benefits (ashwagandha shows small effects), but nothing approaching the marketing claims.

Verdict: Not recommended. If you suspect low testosterone, see a doctor rather than buying supplements.

Fat burners

The claim: Dramatically increase metabolism and fat burning.

The reality: Most fat burners are primarily caffeine with added ingredients that have minimal effect. Any small metabolic boost is easily negated by eating slightly more. Calories in vs. out remains the fundamental driver of fat loss.

Some ingredients (like caffeine) do modestly increase metabolic rate, but you can get the same effect from coffee at a fraction of the price.

Verdict: Not recommended. Focus on diet and training for fat loss. Save your money.

Detox supplements

The claim: Remove toxins from your body and improve health.

The reality: Your liver and kidneys already detoxify your body. "Detox" supplements have no meaningful evidence supporting their claims. The concept of needing to "detoxify" from normal life is largely marketing fiction.

Verdict: Complete waste of money.

How to evaluate supplements

When considering any supplement, ask:

1. What's the mechanism? Does it make biological sense?
2. What's the evidence? Are there multiple high-quality human trials?
3. Who funded the research? Be skeptical of studies funded by supplement companies
4. What's the effect size? Even "significant" effects may be too small to matter practically
5. What's the cost-benefit? Is it worth the money compared to alternatives?

Red flags to watch for

• Claims that sound too good to be true
• Proprietary blends hiding ingredient amounts
• Cherry-picked testimonials and before/after photos
• "Doctors don't want you to know" marketing
• Referencing only animal or cell studies

Building a sensible supplement stack

For most people

1. Vitamin D: 1,000-4,000 IU daily (especially in winter)
2. Protein powder: If needed to meet targets
3. Creatine: 3-5g daily (if doing resistance training)

Monthly cost: Approximately £15-25

For serious athletes

Add to the above:

• Caffeine: Pre-workout as needed
• Omega-3s: If not eating fatty fish
• Magnesium: If sleep or recovery is an issue

Monthly cost: Approximately £25-40

What you don't need

Most pre-workouts (just use coffee), BCAAs, testosterone boosters, fat burners, detoxes, most "greens" powders.

Summary

• Only a few supplements have strong evidence: Creatine, protein, caffeine, vitamin D
• Many popular supplements have weak evidence: Save your money
• Food should always come first: Supplements fill gaps, they don't replace diet
• Marketing claims often exceed evidence: Be skeptical
• Simple stacks work: You don't need 15 different products

The best thing you can do for your health and fitness is eat well, train consistently, sleep adequately, and manage stress. Supplements are, at best, the final 1-2% of optimisation.

References

1. Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation. J Int Soc Sports Nutr. 2017.
2. Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018.
3. Guest NS, et al. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021.
4. Holick MF, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011.
5. Wolfe RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? J Int Soc Sports Nutr. 2017.