Study archive · page 25

In pooled results from randomised trials, zinc supplementation taken on its own was linked to colds ending about 2.25 days sooner in healthy adults. Other micronutrients, including vitamin D and vitamins A and E, did not appear to prevent colds or ease symptom severity.

⚠What it shows: Worth taking seriously: this sweep of all the trial evidence pooled 10 zinc trials in healthy adults, and the 2.25-day saving appeared only when zinc was taken by itself. The plausible range around that figure is wide, so the exact size of the benefit is not pinned down.Systematic review · Am J Trop Med Hyg

Pooled data from ten randomised trials in 211 older women show that adding creatine to resistance training improves upper-body strength, with both upper- and lower-body strength improving when programmes lasted at least 24 weeks. Measures of muscle mass did not change.

⚠What it shows: Promising but thin: results pooled from ten trials covering just 211 older women, and the authors themselves call for higher-quality studies to confirm it. Strength improved, yet muscle size showed no measurable change.Meta-analysis · Nutrients

Across 80 randomised crossover studies in young healthy adults, dietary nitrate supplementation produced a small but clear improvement in exercise performance. The benefit appeared in recreationally active young men but was not observed in women-only studies or in well-trained endurance athletes.

⚠What it shows: About as solid as supplement evidence gets for the headline effect, pooling 80 trials, but the boost is small and the studies were mostly of young healthy men. Only six tested women alone, so the blank result in women may simply reflect missing data.Meta-analysis · Med Sci Sports Exerc

A systematic review of 23 studies found beetroot juice can improve cardiorespiratory endurance in athletes, increasing efficiency and time to exhaustion at submaximal intensities, though combining it with other supplements such as caffeine may undermine the effect.

⚠What it shows: Fairly persuasive but not settled: a sweep of 23 studies in athletes mostly pointed the same way, though the authors note some findings contradict each other. No numbers were pooled, so the size of the benefit is unclear.Systematic review · Nutrients

Across 19 randomised trials of active people aged 14 to 39, soy protein produced lean mass gains identical to whey in some studies and showed potential endurance performance benefits at doses of 10 to 53.3 g, while its effects on testosterone and cortisol were inconsistent.

⚠What it shows: A sweep of all 19 randomised trials on this in active people aged 14 to 39, but the picture is patchy: soy matched whey only in some studies, hormone findings flipped between trials, and results on aerobic capacity conflicted. This is soy holding its own rather than beating whey.Systematic review · Sports Med

Pooled results from 11 trials in people with diabetes found omega-3 supplements had no significant effect on triglycerides, cholesterol, HbA1c, fasting glucose or inflammation markers. Fasting insulin, insulin resistance and corneal nerve health did improve, though the authors call these findings hypothesis-generating.

⚠What it shows: Take this as a signal, not a verdict: results were pooled from 11 small trials and the reviewers rated the certainty of the evidence as very low to low. The nulls on blood fats and blood sugar are as informative as the insulin finding, but bigger, longer trials are needed before either counts as settled.Review · Curr Dev Nutr

Across 143 randomised trials, creatine supplementation increased body mass by 0.86 kg and fat-free mass by 0.82 kg while reducing body fat percentage by 0.28 points; effects were larger when a maintenance dose was used or resistance training was performed alongside.

⚠What it shows: About as strong as supplement evidence gets: results pooled from 143 trials where people were assigned at random, with unusually consistent findings. Even so, the average gain was under a kilogram of lean mass, and one author has ties to a creatine manufacturer.Meta-analysis · J Int Soc Sports Nutr

Across 21 randomised trials involving 2020 women in the menopausal transition and after menopause, physical activity reduced both depressive and anxiety symptoms compared with controls, with low and moderate intensity exercise proving similarly effective.

⚠What it shows: The direction is convincing, the exact size less so: results pooled from 21 trials of 2020 women showed clear mood benefits, but the trials disagreed with each other a lot about how large they are. The anxiety findings also rest on fewer studies than the depression ones.Meta-analysis · Int J Behav Nutr Phys Act

In four randomised trials of 176 women with PCOS and obesity, GLP-1 drugs reduced waist circumference by 5.16 cm, BMI by 2.42 points and total testosterone compared with placebo, but did not significantly change total cholesterol or insulin resistance scores.

⚠What it shows: Promising but thin: just four trials and 176 women in total, so these numbers could easily move as larger trials report. Insulin resistance and cholesterol showed no clear change, and mild stomach side effects such as nausea were common.Meta-analysis · J Diabetes Complications

Across 29 randomised comparisons in 1529 people with PCOS, weight loss interventions improved insulin resistance, free androgen levels and menstrual frequency compared with usual care, but showed no clear improvement in hirsutism or quality of life.

⚠What it shows: A careful sweep of the trials but a messy evidence base: 29 comparisons in 1529 women mixed diets, GLP-1 drugs and other medicines, and the studies disagreed with each other a lot. Nearly half were at high risk of bias, so the exact sizes of the benefits are soft.Meta-analysis · Ann Intern Med

Aerobic exercise reduced period pain intensity and shortened pain duration by an average of 12.53 hours in results pooled from 16 randomised trials involving 918 adolescents and young women with primary dysmenorrhoea. Pilates, low-intensity formats and a frequency of two or fewer sessions per week showed the largest effects.

⚠What it shows: Encouraging but messy: results pooled from 16 trials in 918 adolescents and young women, yet the trials disagreed with each other considerably on how big the relief was. The direction is consistent; the exact size of the benefit is not settled.Meta-analysis · Acta Obstet Gynecol Scand

Pooled results from 12 randomised trials show resistance training significantly improves maximal oxygen uptake and both upper and lower body strength in healthy postmenopausal women; the authors back a frequency of 3 days per week in 60-min sessions. Effects on bone density and body composition remain debated.

⚠What it shows: Solid footing: results pooled from 12 trials where healthy postmenopausal women were assigned at random to resistance training or a control group, and the strength gains were large and consistent. Bone density and body composition are still contested, so this is a fitness finding, not a fracture prevention one.Meta-analysis · Climacteric

In pooled trials, exercise improved fasting insulin, insulin resistance, total and LDL cholesterol, triglycerides, aerobic fitness, waist circumference and body fat in women with PCOS compared with usual care, though the underlying evidence was graded low or very low quality.

⚠What it shows: Encouraging but fragile: pooled results from 18 trials in women with PCOS, mostly graded low or very low quality, with modest effects and wide margins that shifted when single trials were added or removed.Meta-analysis · Syst Rev

Nutritional interventions modestly reduced depressive and anxiety symptoms in women during and after the menopausal transition across 32 placebo-controlled trials, but the studies varied so much that the true effect of any single approach remains unclear.

⚠What it shows: Promising but murky: results pooled from 32 placebo-controlled trials, yet the diets, supplements and mood questionnaires varied so much that the studies disagreed with each other, and the authors say the real effect of any one approach is still unclear.Meta-analysis · Menopause

Pooled results from 29 trials in 1,227 adults aged 60 and over show HIIT and moderate continuous cardio produced similar gains in fitness, blood pressure, blood sugar and body fat percentage, but only HIIT significantly reduced fat mass and waist circumference and improved a cognitive test.

⚠What it shows: Strong overall: results pooled from 29 trials in 1,227 people aged 60 and over. HIIT's extra edge appeared mainly in the better controlled trials, so exactly how big that advantage is remains open.Meta-analysis · Arch Gerontol Geriatr

In older adults, high-intensity interval training improved peak oxygen uptake more than moderate-intensity continuous training across pooled randomised trials, alongside favourable changes in muscle power, cardiac function, blood triglycerides and glucose. Subgroups suggested programmes longer than 12 weeks at 2 sessions per week worked best.

⚠What it shows: Reasonably firm: results pooled from randomised trials in older adults, so the direction is trustworthy. The fitness edge over steady cardio was modest, though, and the training recipes varied widely from study to study, so the ideal formula is a hint rather than a rule.Meta-analysis · Exp Gerontol

Pooled results from 32 randomised trials covering 47,332 people with type 2 diabetes or obesity linked tirzepatide to a 60% lower risk of hypertension-related adverse events but roughly two and a half times the risk of hypotension-related events, especially at higher doses. Semaglutide showed no significant link with blood pressure events in either direction.

⚠What it shows: Strong pooled evidence: 32 trials where people were assigned at random, covering 47,332 people with type 2 diabetes or obesity. The catch is that these were side effects logged during drug trials built for other questions, not studies designed to measure blood pressure itself.Meta-analysis · Endocrine

In a pooled comparison of 27 randomised trials covering 15,584 people with obesity or overweight, retatrutide 12 mg cut body weight by 22.10% versus placebo, ahead of retatrutide 8 mg at 20.70% and tirzepatide 15 mg at 16.53%, making multi-hormone agonists more effective than single GLP-1 drugs including semaglutide.

⚠What it shows: About as strong as it gets short of direct head-to-head trials: results pooled from 27 trials of 15,584 people, though most drugs were compared through a shared placebo rather than against each other directly. People with type 2 diabetes lost noticeably less weight on the same drugs.Meta-analysis · Metabolism

A meta-analysis of eleven trials found muscle growth was similar whether sessions started with big compound lifts or isolation exercises, but strength gains were largest in whichever exercises were performed first in the session.

⚠What it shows: Solid as far as it goes: results pooled from eleven good to excellent quality trials all point the same way. It cannot say whether the pattern holds over years of training or in every type of lifter, and muscle growth was measured in different ways across the trials.Meta-analysis · Eur J Sport Sci

Cold water immersion aided recovery of jump and sprint performance 24 hours after team sport and reduced perceived fatigue at 72 hours in pooled data from 23 studies; neither cold water immersion nor contrast water therapy improved perceived muscle soreness.

⚠What it shows: Reasonable evidence for athletes: results pooled from 23 studies with 606 team sport players. The benefits were selective, with some performance and fatigue measures improving while perceived soreness did not, so it is not a blanket recovery fix.Meta-analysis · J Strength Cond Res

Aromatherapy delivered by inhalation or massage significantly lowered anxiety scores across 32 randomised trials, regardless of the cause of the anxiety, with state anxiety falling by about 5 points on average.

⚠What it shows: Worth some weight, but the benefit is modest: results pooled from 32 trials showed roughly a 5 point drop on a standard anxiety questionnaire. The trials covered patients with all sorts of anxiety, and none of them settled which oil or what dose works best.Meta-analysis · J Affect Disord

Across nine studies of 9,662 adults, people with hypothyroidism had 2.73 times the odds of cardiovascular death compared with those with normal thyroid function, yet showed no increased odds of developing cardiovascular events in the first place.

⚠What it shows: Take the mortality link seriously but not as proof of cause: results pooled from nine studies that followed 9,662 adults rather than testing any treatment. The absence of a link with developing heart disease was not significant, which the authors stress is not the same as showing no effect.Meta-analysis · Endocrine

Dietary fibre interventions raised the abundance of Bifidobacterium and Lactobacillus species and faecal butyrate in healthy adults, but did not change overall microbial diversity, in results pooled from 64 randomised trials with 2099 participants. Fructans and galacto-oligosaccharides drove the largest bacterial gains.

⚠What it shows: Solid ground: results pooled from 64 trials in 2099 healthy adults, so the bacterial shifts look real. But the fibres and lab methods varied between studies, and higher counts of these bacteria are not yet proof of better health.Meta-analysis · Am J Clin Nutr

Across 19 randomised trials (456 people doing the exercises, 470 controls), pelvic floor muscle strengthening reduced low back pain intensity more than control care, with the biggest reductions in postpartum and pregnant women.

⚠What it shows: Decent evidence with a wobble: results pooled from 19 trials all pointed towards less pain after pelvic floor training, but the trials disagreed with each other a lot, so the true size of the benefit is uncertain. The clearest signal came from women during and after pregnancy, so it may not transfer equally to everyone else.Meta-analysis · Neurol Sci