Heart attacks happen when blood flow to a section of heart muscle is suddenly blocked, and the heart can’t get oxygen.
The NHS this week warned the cold weather could trigger an increase in heart attacks.
A new study may have brought scientists a step closer to understanding why they happen when they do.
Most cases take place in the early morning between 1am and 5am, and these also tend to be more severe than those that happen later in the day.
Researchers at the University of Surrey and Cambridge’s MRC Laboratory of Molecular Biology now believe it is down to fluctuating potassium levels.
The mineral is thought to affect the circadian rhythms in red blood cells – responsible for transporting oxygen around the body – which could go on to cause an attack.
Circadian rhythms are a 24-hour internal body clock that controls physical, mental and behavioural changes over a daily cycle.
Red blood cells, the scientists discovered, had their own circadian rhythms that served to alter their activity between days and night.
This was like other cells in the body. However, in contrast to other cells, red blood cells do not have DNA or a ‘clock gene’.
Until now, it had been unknown how their activity was controlled.
In the new study, researchers realised there was significant variation in the potassium levels in the cells, and this corresponded with the circadian rhythms.
Levels of potassium increased during the day, and then lowered at night.
When the researchers themselves altered the potassium levels, they discovered they were negatively impacting on the circadian rhythm of a cell.
They believe the findings that red blood cells are influenced by circadian rhythm could now help them understand why heart attacks mostly take place in the morning.
Dr Fatima Labeed, lead researcher and senior lecturer at the University of Surrey, said: “This exciting discovery gives us a unique insight into the workings of red blood cell membrane physiology and its clock mechanism – where ion transport seems to be of particular importance.
“The study of circadian rhythms in red blood cells can potentially help us understand when and why heart attacks mostly occur during the morning.
“We will be looking into this further in our forthcoming studies.”
Potassium is best known as a nutrient found in avocado, banana and sweet potato.
However, there is no suggestion that the amount of potassium consumed through diet can play a part in triggering or preventing a heart attack.
Heart attack symptoms include chest pain and an overwhelming sense of dread.