Swimming

What it is

Swimming is a whole-body aerobic exercise done in water, from gentle lengths to hard interval sessions [1]. The studies here cover lap swimming and water exercise classes (often called aquatic exercise); some reviews pool the two [2][3]. Water takes weight off the joints, which is why swimming is often suggested for older adults and people with osteoarthritis [4][5].

How it might work

Researchers propose that swimming lowers blood pressure in the same ways as other aerobic exercise, partly by making arteries less stiff and helping blood vessels widen [6]. In a 20-week trial, the blood pressure drop came with lower pulse wave velocity, a stiffness measure, and in a 12-week trial a vessel-function measure (flow-mediated dilation) improved [6][4]. These are proposed pathways; the trials were not designed to test that link directly.

What the research says

Blood pressure. A 2018 meta-analysis pooled 14 randomised trials with 452 adults doing water exercise or no exercise: systolic pressure fell by 8.4 mmHg and diastolic by 3.3 mmHg on average, and the drops were significant in people with high blood pressure and in programmes that were not swimming-only [2]. The review reported high heterogeneity for systolic pressure, meaning trial results varied widely [2]. A second 2018 meta-analysis of upright water training (water aerobics and similar) found lower systolic (effect size 1.47) and diastolic (0.92) readings than no training; the systolic effect was significant in people with high blood pressure but not in prehypertension, and systolic drops matched land training, though diastolic drops were a little smaller than with land training in people with high blood pressure [3]. In type 2 diabetes, a 2023 meta-analysis of 12 studies found systolic pressure 5.55 mmHg and diastolic 4.99 mmHg lower after water training and similar results to land training [7].

Swimming trials show the same direction. In 43 adults over 50 with prehypertension or stage 1 hypertension, 12 weeks of swimming cut casual systolic pressure from 131 to 122 mmHg, with lower daytime and central readings and a 21% rise in carotid artery compliance [4]. In 100 postmenopausal women with stage 2 hypertension, 20 weeks of swimming lowered systolic and diastolic pressure by 9 mmHg each and reduced arterial stiffness [6]. In 52 postmenopausal women with hypertension, 12 weeks of water aerobics lowered systolic pressure from 136 to 124 mmHg, about the same as the land-training group, with no change in controls [8]. High-intensity interval swimming and longer steady swimming both lowered systolic pressure (6 and 4 mmHg) in 62 women with mild hypertension [1]. In patients with osteoarthritis, 12 weeks of swimming improved artery function at least as much as cycling [5].

One session also matters: after a 45-minute water workout, 24 older women with hypertension had systolic pressure about 5 mmHg lower over the following 21 hours than after a land session [9]. A 2022 pooled analysis of four small trials found no 24-hour difference versus land exercise but night-time systolic pressure 8.6 mmHg lower after water exercise [10]. In a 2026 dose-response review of 74 trials in mostly postmenopausal women, water exercise gave the largest estimated drops (11.63 mmHg systolic, 7.73 mmHg diastolic at the dose studied), but the estimate came from only three study arms and the authors call it exploratory [11].

Longevity. Pooled longitudinal studies found swimming associated with 24% lower all-cause mortality [12]. Large cohorts agree less: in about 111,000 US adults followed for decades, swimming was the one activity with no link to lower death rates [13]; a 272,550-person cohort found a small 5% lower risk [14]; and among 10,218 older men, higher-intensity, higher-volume swimming was linked to a 19% lower risk that did not reach statistical significance [15]. The 2024 review also reported better body composition and blood lipids with swimming (p < 0.01) [12]; one cross-sectional study found slightly higher body mass index and waist size in swimmers, which cannot show cause [16].

Blood sugar and cognition. In adults with type 2 diabetes, water exercise lowered HbA1c by 0.96% versus no exercise across nine small trials, and matched land exercise [17]. A 2026 review of swimming in older adults found 17 mostly cross-sectional studies, of which six reported significantly better cognitive function, including one 31-person randomised trial in suspected mild cognitive impairment [18]; two small randomised trials and two quasi-experimental studies reported better mood and behavioural symptoms (for example, anxiety and depression scores) [18].

Doses used in studies

Trials used 45 to 60 minutes of exercise, three or four times a week, for 12 to 20 weeks [9][1][6]. One interval programme used 6 to 10 bursts of 30 seconds of hard swimming with 2 minutes of recovery, three times a week [1]. A 16-week study swam 2 hours, three times a week, in water at 29 to 33 °C [19]. A single session in the post-exercise study lasted 45 minutes at moderate intensity [9]. These are doses used in research, not recommendations.

Safety and interactions

Side effects and upper limits. The trial reports cited here do not describe serious harms, and no toxic or upper training limit was reported [6][4]. Rare risk. Swimmers, especially in open water or races, can develop swimming-induced pulmonary edema (fluid in the lungs). A 2026 review of triathlon reports put the prevalence under 1.5% and listed risk factors including female sex, age over 50, high blood pressure, cold water and wetsuit compression [20]. Medicines. No medicine interactions were reported in the studies read; in a 12-week trial, women kept taking their blood-pressure medicines and still had lower pressure [8]. Pregnancy and breastfeeding. Two trials found no more complications with water exercise in pregnancy than usual care [21][22]; a pooled analysis of 10 trials (1,949 women) found no difference in birth weight, Apgar scores or preterm birth [22], and a small 6-week programme in pregnant women was linked to lower blood pressure and better fluid balance [23]. No breastfeeding data were found. Conditions. Trials of water training excluded people with heart disease other than high blood pressure [3]. People with uncontrolled high blood pressure, a heart condition, or who cannot swim should ask a doctor before starting. No kidney, liver or bleeding-disorder data were found in the studies read.

Caveats and open questions

Blood pressure is a marker: no trial measured heart attacks, strokes or deaths, so the drops may not translate into fewer health events [2].

Results conflict in places. A 6-month trial of 116 older women with normal pressure found swimming raised systolic pressure by 4.4 mmHg (lying down) and 6.0 mmHg (standing) compared with walking [24]. The main meta-analysis reported high heterogeneity for systolic pressure, and its significant subgroup findings were in people with high blood pressure and in non-swimming programmes [2]. Upright water training lowered systolic pressure in hypertension but not in prehypertension [3]. The 2026 water-exercise estimate rests on three study arms [11], and that review rated its certainty very low to low [11].

Cohort results for longer life disagree [12][13]. Trials were small: 452 people across 14 trials in the largest pool [2], 24 women in the single-session trial [9]. Longer trials are needed to see whether swimming's pressure drops lead to fewer heart attacks and strokes.