Drinking a single glass of water before going to bed may seem like a minor habit, but scientific research suggests it can play a meaningful role in supporting cardiovascular and brain health. Multiple medical studies and clinical observations indicate that proper hydration overnight helps maintain healthy blood circulation, which may lower the risk of stroke and heart attack—particularly in older adults and individuals with existing cardiovascular risk factors.

This potential benefit is closely tied to how hydration influences blood thickness, circulation efficiency, and the workload placed on the heart during sleep.

What Happens to Your Body During Sleep

During sleep, the body goes several hours without fluid intake. As a result, mild dehydration can develop overnight, especially in people who:

• Sweat during sleep

• Live in warm or humid climates

• Consume caffeine or alcohol in the evening

• Do not drink enough water throughout the day

When dehydration occurs, blood becomes more concentrated and viscous. Thicker blood flows more slowly through blood vessels, increasing resistance and raising the likelihood of clot formation—one of the primary causes of ischemic strokes and heart attacks.

How Water Supports Heart and Brain Health

Drinking a small amount of water before bedtime helps the body:

• Maintain adequate blood volume

• Prevent excessive blood thickening

• Promote smoother blood circulation

• Reduce strain on the heart during nighttime rest

Medical research has consistently linked elevated blood viscosity with increased cardiovascular risk. By staying properly hydrated, blood flows more easily through arteries, easing pressure on the heart and supporting overall vascular health while you sleep.

Morning Cardiovascular Risk and Hydration

Heart attacks and strokes occur more frequently in the early morning hours. This increased risk is associated with several natural physiological changes, including:

• A rise in blood pressure upon waking

• Hormonal shifts that encourage blood clotting

• Fluid loss and dehydration during sleep

Drinking water before bed helps counteract overnight fluid depletion, which may reduce cardiovascular stress in the morning when the body is most vulnerable.

Supporting Evidence From Medical Observations

Clinical observations from Japan and several European countries have long emphasized the importance of nighttime hydration, especially for older adults. In some healthcare settings, patients at higher risk of stroke are advised to drink a small glass of water before bedtime and again after waking.

While water alone cannot prevent cardiovascular disease, long-term studies consistently show that chronic dehydration is associated with poorer blood vessel function and increased cardiovascular strain.

Finding the Right Balance

Moderation is key. The recommendation is one small glass of water, not excessive fluid intake. Drinking too much before bed may:

• Interrupt sleep due to frequent nighttime urination

• Pose risks for individuals with kidney disease, heart failure, or fluid-balance disorders

For most healthy adults, 150–250 ml (about one glass) is considered sufficient and safe.

Who May Benefit the Most

This simple habit may be particularly helpful for:

• Older adults

• People with high blood pressure

• Individuals with circulation or blood-thickening issues

• Those who struggle to stay hydrated during the day

Anyone with a medical condition or on fluid restrictions should consult a healthcare professional before making changes to their hydration routine.

Not a Replacement for Medical Care

It’s important to be clear: drinking water before bed is not a substitute for medication, medical treatment, or lifestyle changes recommended for preventing heart disease or stroke. Instead, it should be viewed as a supportive habit that complements a healthy diet, regular exercise, and proper medical care.

The Bottom Line

Drinking one glass of water before going to bed helps maintain hydration, supports healthy blood flow, and may reduce cardiovascular strain during the night—factors linked to a lower risk of heart attack and stroke.

It’s a simple, low-cost routine with potential long-term benefits, showing that even small daily habits can contribute meaningfully to heart and brain health.