Can Creatine Supplementation Improve Body Composition and Objective Physical Function in Rheumatoid Arthritis Patients? A Randomized Controlled Trial

The researchers tested whether daily oral creatine monohydrate supplementation could increase muscle mass (lean mass), improve strength, and enhance physical function in people with rheumatoid arthritis (RA). The intervention was:

**Creatine group:** 20g per day (4 x 5g packets) for the first 5 days ("loading phase"), then 3g per day for the remaining 11.5 weeks ("maintenance phase")

**Placebo group:** Identical-tasting flavoured drink powder with no creatine

**Duration:** 12 weeks of supplementation, with follow-up at 24 weeks (12 weeks after stopping)

**Outcomes measured:** Body composition (lean mass, fat mass, bone mass), strength (knee extension and handgrip), physical function (sit-to-stand test, 8-foot up-and-go test, 50-foot walk test), and aerobic capacity

**Sample size:** 40 patients with rheumatoid arthritis (20 creatine, 20 placebo)

**Population:** Adults aged ≥18 years with stable RA (no medication changes in the preceding 3 months)

**Setting:** Outpatient clinics at the Peter Maddison Rheumatology Centre, Llandudno, North Wales, UK; assessments at Bangor University

**Inclusion criteria:** Confirmed RA diagnosis (ACR/EULAR 2010 criteria), eGFR ≥60 mL/min/1.73m² (normal kidney function), no anabolic supplements, no regular high-intensity exercise, not pregnant

**Exclusion criteria:** Cognitive impairment, other cachectic conditions, renal impairment

**Demographics:** Groups were matched for sex and age (stratified into 18-44, 45-59, 60+ years)

**Body composition:** Dual-energy X-ray absorptiometry (DXA) — the gold standard for measuring lean mass, fat mass, and bone mass. Appendicular lean mass (ALM, the sum of arm and leg lean mass) was used as a surrogate for total body muscle mass.

**Intracellular water:** Bioelectrical impedance spectroscopy (BIS) — measures total body water, intracellular water, and extracellular water. This matters because creatine pulls water into muscle cells, so increased intracellular water confirms the creatine was actually taken up by muscle tissue.

**Strength:**

- Isometric knee extensor strength (IKES) — measured on a Humac Cybex dynamometer (a machine that measures force production). Participants sat with hip and knee at 90°, pushed as hard as possible for ~3 seconds. Best of 3 trials per leg, averaged.

- Handgrip strength (HGS) — measured with a Grip-A dynamometer. Participants squeezed maximally while adducting the arm. Best of 3 trials per hand recorded.

**Physical function:**

- Sit-to-stand in 30 seconds (STS-30) — number of full stands from a chair (seat height 43.2 cm) with arms folded across chest

- 8-foot up-and-go test (8'UG) — time to stand, walk 8 feet around a cone, and return to seated position

- 50-foot walk test (50'W) — time to walk 50 feet as quickly as possible

**Aerobic capacity:** Submaximal Siconolfi step test — stepping up and down a 10-inch step at increasing rates (17, 26, 34 steps per minute) until reaching 65% of predicted max heart rate. VO2max estimated from equations.

**Clinical measures:** Disease Activity Score in 28 joints (DAS28), C-reactive protein (CRP) for inflammation

**Timing:** All measures taken at baseline, day 6 (post-loading), week 12 (end of supplementation), and week 24 (12-week follow-up)

### Study Design

This was a **double-blind, randomised, placebo-controlled trial (RCT)** — the gold standard for testing whether a treatment works. The study ran for 24 weeks total: 12 weeks of supplementation followed by 12 weeks of washout (follow-up).

### Randomisation

Randomisation was performed independently by the North Wales Organisation for Randomised Trials in Health (NWORTH), a registered clinical trials unit, using a secure online system. Groups were stratified by sex and age (18-44, 45-59, 60+ years) to ensure balance. This matters because age and sex strongly influence muscle mass and strength, so stratification prevents these variables from confounding the results.

### Blinding

Both the experimenter (TJW) and participants were blinded to supplement assignment until trial completion. The creatine and placebo packets were indistinguishable in appearance, flavouring, and colouring. This is critical because expectation effects can influence both physical performance and self-reported outcomes. Double-blinding eliminates this bias.

### Duration

**Loading phase:** 5 days (20g/day) — standard protocol to rapidly saturate muscle creatine stores

**Maintenance phase:** 11.5 weeks (3g/day) — sufficient to maintain elevated muscle creatine levels

**Total supplementation:** 12 weeks — long enough to detect changes in muscle mass (which typically requires 8-12 weeks)

**Follow-up:** 12 weeks after cessation — to see if effects persist or reverse

### Statistical Approach

Analysis of covariance (ANCOVA) was used, which adjusts for baseline values. This is appropriate because it accounts for individual differences at the start and increases statistical power to detect treatment effects.

### What This Design Can and Cannot Prove

**Can prove:**

Whether creatine causes changes in body composition, strength, and function compared to placebo (causality, not just correlation)

Whether effects persist after stopping supplementation (due to the 24-week follow-up)

Whether the intervention is safe (adverse events monitored)

**Cannot prove:**

Whether creatine works in combination with exercise (participants were asked to maintain routine activity, not to exercise)

Whether effects differ by disease severity (sample too small for subgroup analysis)

Whether longer supplementation (>12 weeks) produces different results

Whether creatine prevents muscle loss (cachexia) over years rather than reversing it

Whether results generalise to people with severe renal impairment (excluded from study)

### Methodological Weaknesses

**Small sample size (n=40):** With only 20 per group, the study may have been underpowered to detect small-to-moderate effects on strength and function. The authors report no power calculation.

**No exercise component:** Creatine's effects on strength are typically amplified when combined with resistance training. Without exercise, the study tests creatine alone, which may underestimate its potential.

**Self-reported adherence:** While packet returns were monitored, there's no objective measure (e.g., blood or urine creatine levels) confirming participants actually took the supplement.

**Short loading phase:** 5 days at 20g/day may not fully saturate muscle creatine stores in all individuals, especially those with low baseline levels.

**No dietary control:** Participants were asked to maintain usual diet, but dietary protein intake (which affects muscle protein synthesis) was not measured or controlled.

### Primary Outcome: Body Composition

**Appendicular lean mass (ALM):** Increased by 0.52 kg (± 0.13 kg) in the creatine group versus placebo (P = 0.004). This was the primary endpoint and was statistically significant.

**Total lean mass:** Increased by 0.60 kg (± 0.37 kg) in creatine versus placebo (P = 0.158). This was not statistically significant, meaning the increase could be due to chance.

**Intracellular water (ICW):** Increased by 0.64 L (± 0.22 L) in creatine versus placebo (P = 0.035). This confirms creatine uptake into muscle cells, as creatine osmotically draws water into cells.

**Fat mass:** No significant changes reported.

### Secondary Outcomes: Strength

**Isometric knee extensor strength (IKES):** No significant difference between creatine and placebo (P = 0.408)

**Handgrip strength (HGS):** No significant difference (P = 0.833)

### Secondary Outcomes: Physical Function

**Sit-to-stand in 30 seconds (STS-30):** No significant difference (P values ranged from 0.335 to 0.764 across time points)

**8-foot up-and-go test (8'UG):** No significant difference

**50-foot walk test (50'W):** No significant difference

### Secondary Outcomes: Aerobic Capacity and Clinical Measures

**Estimated VO2max:** No significant changes

**Disease Activity Score (DAS28):** No significant changes

**C-reactive protein (CRP):** No significant changes

### Safety

No treatment-related adverse effects were reported. Creatine was well-tolerated.

The key finding is that creatine increased muscle mass by about **half a kilogram (0.52 kg)** over 12 weeks. To put this in perspective:

This is roughly the amount of muscle a healthy young adult might gain from 4-6 weeks of consistent resistance training

For an RA patient with rheumatoid cachexia (muscle wasting), this represents a meaningful reversal of muscle loss — but it's modest

The 0.52 kg increase in appendicular lean mass is approximately 2-3% of total muscle mass in a typical adult

However, this increase in muscle mass **did not translate into any measurable improvement in strength or physical function**. The effect on strength was essentially zero — the P-values (0.408 for knee strength, 0.833 for handgrip) indicate no signal whatsoever. Similarly, the physical function tests showed no improvement (all P > 0.3).

This is surprising because, in healthy populations, a 0.5 kg increase in muscle mass typically produces at least a small improvement in strength. The fact that it didn't here suggests that in RA patients, the newly added muscle tissue may be qualitatively different (e.g., lower quality, more fibrotic, or less innervated) or that the muscle was added in a way that doesn't contribute to force production.

The intracellular water increase (0.64 L) confirms that creatine was actually taken up by muscle cells — so the lack of strength effect isn't due to poor absorption. This is an important negative finding: creatine can increase muscle mass without improving function in this population.

### What the Authors Acknowledge

Small sample size (n=40) limits statistical power to detect smaller effects on strength and function

No exercise component — creatine's benefits are typically amplified by resistance training

Self-reported adherence without biochemical verification

Short loading phase may not have fully saturated muscle creatine stores

### What a Critical Reader Would Note

**No power calculation:** The authors don't report how many participants would be needed to detect meaningful effects on strength or function. With 20 per group, the study may have been underpowered for secondary outcomes.

**No measure of muscle quality:** DXA measures quantity (mass) but not quality (e.g., muscle fibre type, fat infiltration, neuromuscular activation). The added mass could be lower-quality tissue.

**No exercise standardisation:** Participants were asked to maintain routine activity, but this wasn't objectively measured. Variability in physical activity could mask or inflate effects.

**Short duration for strength gains:** While 12 weeks is sufficient for muscle mass changes, strength gains from creatine alone (without training) may require longer.

**Population specificity:** Results may not generalise to RA patients with severe cachexia, those on different medications, or those who are physically active.

**No dietary protein measurement:** Protein intake strongly influences muscle protein synthesis. If the creatine group happened to consume more protein, this could confound results.

**Industry funding:** Funded by Betsi Cadwaladr University Health Board (public funding), not supplement industry — this is a strength, not a limitation.

**Single-centre study:** Results may not replicate in other settings or populations.

For someone running their own n=1 experiment (testing creatine for yourself):

### What to Test

**Intervention:** Creatine monohydrate powder

**Dose:** 20g/day (4 x 5g doses) for 5 days loading, then 3g/day maintenance

**Comparator:** No supplement, or a placebo (e.g., flavoured water)

**Duration:** Minimum 12 weeks (8 weeks may be sufficient for muscle mass, but 12 is safer)

### Minimum Meaningful Duration

**For muscle mass changes:** 8-12 weeks. You won't see changes in the first 2-4 weeks.

**For strength changes:** 12+ weeks if not combining with exercise. If combining with resistance training, 8 weeks may suffice.

**Loading phase:** 5 days at 20g/day is standard, but some people respond to lower doses (5-10g/day for 2-3 weeks)

### What to Measure

**Primary metric:** Body composition — ideally DXA scan (gold standard) or bioelectrical impedance (BIA) if DXA unavailable. Measure at baseline, week 6, and week 12.

**Secondary metrics:**

- Strength: Grip strength (handgrip dynamometer, ~$30-50) and leg strength (e.g., 30-second sit-to-stand test)

- Function: Timed up-and-go, 50-foot walk time, or stair climb test

- Subjective: Energy levels, fatigue, ability to perform daily activities (use a 1-10 scale daily)

**Confirmation metric:** If you have access to BIA, track intracellular water — a rise confirms creatine uptake

### Key Confounds to Control For

**Dietary protein intake:** Keep protein consistent throughout the experiment (track with an app like MyFitnessPal). Aim for 1.2-1.6 g/kg body weight per day.

**Physical activity:** Keep exercise consistent. If you start a new training program during the experiment, you won't know if changes are from creatine or training.

**Hydration status:** Creatine increases water retention. Measure body weight at the same time of day, after voiding, and fasted.

**Medication changes:** If you're on RA medication, don't change it during the experiment without medical supervision.

**Time of day:** Take creatine at the same time each day (post-workout is optimal if exercising)

**Caffeine:** Some evidence suggests caffeine may blunt creatine uptake. Avoid caffeine within 1 hour of taking creatine.

### What a Positive Result Would Look Like

**Muscle mass:** Increase of 0.3-0.8 kg in lean mass over 12 weeks (measured by DXA or BIA)

**Intracellular water:** Increase of 0.3-0.7 L (measured by BIA)

**Strength:** Improvement of 5-15% in grip strength or sit-to-stand repetitions (if also training)

**Function:** Improvement of 5-10% in timed walk or up-and-go tests (if also training)

**Subjective:** Reduced fatigue, easier performance of daily tasks

### Important Caveats

**This study found NO strength or function benefit from creatine alone** — if you don't combine it with resistance training, you may gain muscle but not get stronger

**Creatine is safe** for people with normal kidney function (eGFR ≥60), but check with your doctor if you have kidney issues

**Weight gain of 1-2 kg in the first week is normal** due to water retention — this is not fat gain

**Some people are "non-responders"** to creatine (about 20-30% of the population have high baseline muscle creatine and don