Of Hot Tubs and Hypertension

Abstract & Commentary

Synopsis: People with treated hypertension who use hot tubs will experience a fall in blood pressure equivalent to normotensive people.

Source: Shin TW, et al. CMAJ. 2003;169:1265-1268.

Recruiting 21 patients with hypertension from the Cardiovascular Risk Factor Reduction Unit of the University of Saskatchewan and 23 controls, Shin and colleagues tested the hypothesis that hot-water immersion would cause greater blood pressure changes in hypertensive patients than in normotensive controls. They excluded patients who had had a stroke, transient ischemic attack, myocardial infarction, or unstable angina within 6 months of starting the study. The hypertensive patients were treated with a variety of antihypertensives, including thiazide diuretics, ACE-inhibitors, angiotensin-receptor blockers, and ß-blockers. Patients were on no more than 3 drugs and were considered to be "under good control." All subjects had their blood pressure (BP) and heart rate (HR) measured 3 times after sitting for 10 minutes, and then again 3 times at 1, 5, and 10 minutes after immersion in a hot tub at 40°C (104°F). This routine was repeated a third time after leaving the hot tub and sitting for 10 minutes. They completed a symptom questionnaire before and after immersion.

The 2 groups were not matched for age (60.6 vs 43.0 years old) or sex (86% female vs 61% male), with hypertensive patients being older and "maler." They were similar in body mass index (25.9 vs 23.0). As might be expected, the hypertensive patients had higher mean systolic (144.8 vs 130.0 mm Hg) and mean diastolic BP (92.7 vs 83.1 mm Hg) than the normotensive subjects. They also had a higher mean resting HR (83.3 vs 74.7 beats/min [BPM]).

Immediately after immersion, both groups experienced a drop in systolic and diastolic BP (26.3/25.3 vs 21.8/24.4 mm Hg) and a rise in HR (5.2 vs 12.9 BPM); only the rise in HR was statistically significant. The rise in HR remained statistically significant even after excluding the patients using ß-blockers. BP and HR returned to normal in both groups during the post-immersion rest phase. No adverse events (including chest pain and palpitations) were reported, except for very mild headache or dizziness.

Comment by Allan J. Wilke, MD

My first thought after reading this study was, "Why didn’t I do this?" This is one of those elegantly done studies that answer a simple clinical question. Anyone who has ever used a hotel or health club hot tub has seen the posted warnings about consulting a physician before using if you are hypertensive, pregnant, or suffer from heart disease or diabetes. If one of my hypertensive patients had asked me if it was all right for them to use a hot tub, I’d have scratched my head and said I wasn’t sure. Now I can say with some confidence that it is OK, as long as the hypertension is controlled. In the spirit of holistic medicine and full disclosure, I would also have to make sure my patient knew about other conditions associated with hot tubbing. Hot tub and hot bath safety and adverse effects have been studied in other settings, including coronary artery disease,1 Mycobacterium avium complex hypersensitivity pneumonitis,2 legionellosis,3 Acanthamoeba keratitis,4 epilepsy,5 headache,6 multiple sclerosis,7 Pseudomonas aeruginosa folliculitis,8 miscarriage,9 and neural tube defects.10

While elegant, this study isn’t flawless. You can argue that a mean BP of 144.8/92.7 isn’t anyone’s idea of "good control." The subjects and controls differed in ways other than BP. Since Shin et al did not give a racial/ethnic breakdown of their subjects (but you may presume that they were Canadian), you may be reluctant to apply these results to your patients.

Hot-water immersion causes these hemodynamic changes through peripheral vasodilatation. Shin et al caution applying these results to patients taking oral or transcutaneous nitrates. None of their subjects were using these drugs, and, theoretically, they could cause additional vasodilatation and a further drop in BP. The same might be said about other vasodilators, including the selective phosphodiesterase type 5 inhibitors (sildenafil [Viagra®]) and others.

Dr. Wilke, Assistant Professor of Family Medicine, Medical College of Ohio, Toledo, OH, is Associate Editor of Internal Medicine Alert.


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2. Cappelluti E, et al. Arch Intern Med. 2003;163:845-848.

3. Thomas DL, et al. Arch Intern Med. 1993;153:2597-2599.

4. Samples JR, et al. Arch Ophthalmol. 1984;102:707-710.

5. Bebek N, et al. Epilepsia. 2001;42:1180-1184.

6. Liao YC, et al. Cephalalgia. 2003;23:854-859.

7. Berger JR, Sheremata WA. JAMA. 1983;249:1751-1753.

8. MMWR Morb Mortal Wkly Rep. 2000;49:1087-1091.

9. Li DK, et al. Am J Epidemiol. 2003;158:931-937.

10. Milunsky A, et al. JAMA. 1992;268:882-885.