Supplements… The Fact, Fiction and Mystery Debunked

By Dr Timothy Eden, MBBS

Registered Dietitian from Eden Health and Nutrition

Read time approx. 4mins

From magnesium sprays and tablets promising a dreamlike sleep to turmeric shots claiming an invincible immune system, the supplement aisle is brimming with claims.  It’s hard to tell fact from fiction.  These days, supplement aisles resemble modern apothecaries, not just in standard stores and pharmacies but also in supermarkets.  Patients often wonder if these capsules and trinkets truly work or if they’re simply expensive and colourful urine.  While some supplements have solid evidence, others are more myth than medicine.  This guide simplifies the world of popular pills by explaining their intended effects, what research says and when they might be worth considering.

1. Magnesium – sleep, muscles and gut health

UK RNI: Men 300 mg /day   Women 270 mg /day (NHS)

Types matter:

• Magnesium citrate or glycinate – better absorbed and often used for muscle relaxation and sleep.

• Magnesium oxide or hydroxide – poorly absorbed but draws water into the bowel, giving a laxative effect; useful short-term for constipation, not for muscle recovery.

Proposed benefits: Supports over 300 enzyme reactions, including nerve and muscle function. Adequate levels may aid relaxation and improve sleep quality in people with low magnesium status.

Evidence rating: 6 / 10

Some studies show improved sleep and reduced leg cramps in older adults, but evidence in healthy populations is inconsistent.

Reference: Wienecke E et al. Nutrients. 2021; 13(6):1845

2. Vitamin D (+ K2)

UK RNI: 10 µg (400 IU) per day (NICE / NHS)

Proposed benefits: Essential for bone, muscle and immune health. From October–March, UK sunlight is too weak for adequate synthesis, so supplements are recommended for most adults. Vitamin K2 (menaquinone) may help calcium bind to bone rather than arteries, though clear evidence in healthy adults is lacking.

Evidence rating: 8 / 10 for Vitamin D   4 / 10 for K2

Reference: NICE NG187 (Vitamin D: Supplement Use in the General Population)

3. Vitamin C and Zinc – colds and flu

UK RNI: Vitamin C 40 mg /day; Zinc 9.5 mg (men) 7 mg (women)

Proposed benefits: Both nutrients support immune defence and antioxidant protection.

Evidence rating: 5 / 10

Regular vitamin C may slightly shorten cold duration but doesn’t prevent them. High-dose zinc lozenges started within 24 hours of symptoms can cut illness length by about one day, but metallic taste and nausea are common.

Reference: Hemilä H, Chalker E. Cochrane Database Syst Rev. 2013; CD000980

4. Lion’s Mane (Mushroom Powder)

No established RNI – supplements typically 500–3000 mg daily.

Proposed benefits: Marketed to boost focus and “mental energy” through compounds that may promote nerve growth factor (NGF).

Evidence rating: 3 / 10

Animal and small human studies hint at cognitive support, but data are sparse and quality is low. Long-term safety unproven.

Reference: Saitsu K et al. Front Aging Neurosci. 2023; 15:1165953

5. Glucosamine – joint support

Typical dose: 1500 mg glucosamine sulfate daily.

Proposed benefits: Supports cartilage and may reduce osteoarthritis symptoms.

Evidence rating: 6 / 10

Some evidence for mild improvement in knee OA pain, particularly with glucosamine sulfate (not hydrochloride). No strong evidence for prevention of osteoporosis or benefit in other joints.

Reference: Bannuru RR et al. BMJ. 2015; 350:h351

6. Turmeric and Ginger – natural anti-inflammatories

Typical dose: Turmeric (500–1000 mg curcumin with piperine); ginger 1–2 g daily in food or capsule.

Proposed benefits: Curcumin and gingerols have anti-inflammatory and antioxidant actions. Used for arthritis, joint stiffness and gut symptoms.

Evidence rating: 6 / 10

Moderate evidence suggests small improvements in osteoarthritis pain and markers of inflammation, though supplement quality and bioavailability vary widely.

Reference: Daily JW et al. J Med Food. 2016; 19(8):717–729

Final thoughts

Supplements can be genuinely useful when there’s a proven deficiency or when dietary patterns restrict intake, but they should never be seen as a substitute for balanced nutrition, movement, sunlight exposure and good-quality sleep. One exception I routinely highlight in practice is vitamin D — during the autumn and winter months in the UK, supplementation is a no-brainer given our limited UV exposure and the strong evidence supporting musculoskeletal and immune benefits.

With most other supplements, my main priority is safety. Many products interact with prescribed medicines — particularly blood thinners, antiplatelets, statins and certain antihypertensives — and some can alter liver enzyme activity or potentiate bleeding risk. The same caution applies if you’re pregnant, planning pregnancy or breastfeeding, as data for many supplements in these groups are limited or absent.

I also encourage patients to think about affordability and value. Some supplements are marketed with big promises but minimal evidence, and long-term use can become surprisingly expensive. For those who wish to trial something, a structured approach is best: take it consistently for 6–8 weeks, track the specific symptoms you hope to improve, and then make an informed decision about whether it’s genuinely helping or simply adding cost and complexity.

Evidence continues to evolve, but one principle remains constant: check before you swallow. A quick conversation with your GP, pharmacist or dietitian can save a great deal of time, money and potential harm.

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