Blood tends to be thicker, or more viscous, in the morning due to several physiological factors that occur during sleep and the body’s circadian rhythm. Here’s why this happens:

1. Dehydration during sleep: While you sleep, your body goes several hours without water intake, which can lead to mild dehydration. Dehydration reduces the water content in the blood, making it more concentrated and thicker.
2. Hormonal fluctuations: In the early morning hours, the body releases higher levels of certain hormones, like cortisol and adrenaline. These hormones can cause the body to release stored glucose into the bloodstream and increase blood pressure, both of which contribute to thicker blood.
3. Lower body temperature: During sleep, your body temperature drops, which can slow down circulation and cause the blood to become more viscous. This is part of the natural drop in metabolic activity overnight.
4. Higher red blood cell concentration: The body tends to have a slightly higher concentration of red blood cells in the morning, partly because you’re lying down and fluids shift in the body. This can increase the hematocrit (the proportion of red blood cells in blood), making the blood thicker.
5. Platelet activity: In the morning, platelets (the cells involved in blood clotting) are more active. This increased activity can make blood clot more easily and contribute to its thickness.

These factors contribute to an increased risk of cardiovascular events, such as heart attacks or strokes, which tend to happen more often in the early morning. Staying hydrated and adopting healthy lifestyle habits can help reduce the impact of morning blood thickening on heart health.