Sauna and blood flow: what the evidence means after 40

What heat does during a session

As your body manages heat, blood flow to the skin increases and your heart works harder. Small heat-therapy studies have examined changes in vessel function, including nitric-oxide-dependent responses. Those findings help explain why researchers study heat; they do not give you a home test for nitric oxide or establish a benefit from every sauna format. Brunt et al., 2016: nitric oxide pathway

Feeling flushed, sweating heavily, or seeing a higher heart rate on your watch tells you that you are responding to heat. It does not measure arterial health or show that the session is equivalent to a bike ride.

The Finnish research is interesting—and observational

A well-known study followed 2,315 Finnish men who were 42–60 at baseline. More frequent sauna use was associated with lower rates of fatal cardiovascular events and death over follow-up. Because people were not randomly assigned to sauna habits, the study cannot prove that sauna itself caused the difference. Other habits and health differences may contribute. Laukkanen et al., 2015: sauna cohort

That is a reason to take the research seriously without turning its frequency categories into a prescription. It also does not automatically establish the same effects for infrared cabins, steam rooms, or a sauna blanket used at home.

What the controlled trials add

Small trials of repeated passive heating have reported improvements in some vascular measures. But a 2025 review of randomized trials found no clear improvement in most cardiometabolic or vascular markers overall, with a possible systolic blood-pressure benefit in some settings and substantial uncertainty. The evidence is less settled than “sauna prevents heart disease” suggests. Hamaya et al., 2025: heat trials review

Our practical interpretation: treat sauna as an optional habit you enjoy, not the foundation of your cardiovascular plan. Walking, strength work, sleep, and routine medical care deserve space on the calendar first.

Make the routine comfortable rather than competitive

Choose a facility with clear operating and safety guidance. If you are new to sauna, keep the exposure brief, use a less intense location if available, and leave before it becomes a test of endurance. There is no universal number of minutes that is appropriate across room temperatures, humidity levels, health conditions, and individual tolerance.

After exercise, give yourself time to cool down and address thirst before deciding whether more heat sounds sensible. Skipping the sauna after an unusually draining session is a reasonable choice. Do not copy a research heat protocol or attempt to drive your core temperature to a target.

Check the medication and dizziness question

Some medicines change heat tolerance, fluid balance, or blood pressure. CDC heat guidance flags diuretics and several other medication classes; that guidance is about heat exposure broadly, not a validated sauna protocol. Ask a clinician or pharmacist about your own medicines and health history, especially if you have heart disease, low blood pressure, or fainting episodes. Do not stop medicines to use a sauna. CDC: heat and medications

Avoid alcohol, leave if you feel dizzy, nauseated, weak, or unwell, and stand up slowly. Chest pain, fainting, confusion, or severe breathlessness requires urgent attention. Another person tolerating a long session is not evidence that you should stay.

What about erections or a nitric oxide supplement?

The research above does not establish sauna as a treatment for erectile dysfunction or show that pairing it with a supplement improves results. If sexual function has changed persistently, investigate the cause with a clinician. For a simpler decision about heat at home, read our sauna versus hot bath comparison.