Shift work raises the risk of having a heart attack, a major review of working pattern health effects has shown.
Working unsocial hours was found to increase the chances of a heart attack by more than a fifth, with the risk of a stroke rising by 5%.
Shift patterns, especially night shifts, have long been linked to high blood pressure, high cholesterol levels and diabetes.
But experts have disagreed about their association with heart and artery disease.
The new research, the largest analysis of shift work and heart risk to date, pulled together evidence from 34 studies involving more than two million people.
Coronary events - including heart attacks and angina chest pains - and strokes were more common among shift workers.
The chances of "any coronary event" were increased by 24%, and of heart attacks by 23%, while stroke risk was raised slightly by 5%.
Despite the relatively small effect, the impact on a large population could be significant, the authors pointed out.
In Canada, where a number of the researchers were based, 7% of heart attacks could be attributed to shift work.
The scientists, led by Dr Daniel Hackam, from Western University in Canada, wrote in the British Medical Journal: "Shift work is associated with vascular events, which may have implications for public policy and occupational medicine."
Night shifts were associated with the steepest increase in risk for coronary events, 41%. But research found no link between shift work and higher death rates from any cause.
Are you aware of the early warning heart attack signs? Take a look here...
"A dull ache or burning sensation in the epigastrum (upper part of the abdomen). Not all pain typically occurs in the centre of the chest," explains Dr Sanjay Sharma. "The blockage in the heart could cause symptoms similar to indigestion (like fullness, bloating and problems swallowing). If these symptoms longer than two days, seek medical advice."
"Severe pain or pressure sensation around the jaw and neck only could be a sign," says Dr Sanjay Sharma. "If it starts off as a mild discomfort but gradually worsens, seek medical advice immediately."
"Pain in the centre of the upper back is often mistaken for muscular pain, but could be a 'silent heart attack' symptom," says Dr. Sanjay Sharma. "If in doubt, speak to a medical professional as soon as possible."
"Being suddenly short of breath, without any chest pain could be a sign of a herat attack - although it's more likely to occur in elderly people or diabetics. The chest pain could be due to the lack of oxygen to the heart muscle," says Dr Sanjay Sharma. "The breathlessness is often due to the fact that the heart is no longer pumping properly causing the lungs to fill up with fluid."
Dizziness and sweating is a common sign," says Dr Sanjay Sharma. "The sweating is a normal reaction to severe pain and the loss of consciousness may be due to a drop in blood pressure the heart going into a very slow, or very fast electrical rhythm, due to the effects of lack of oxygen."
"If chest pain spreads to your left or right arm, that could be another sign you're having a heart attack. We've heard from heart attack survivors who thought they'd pulled a muscle and waited until the following day before getting themselves to hospital," adds Ellen Mason, senior cardiac nurse from the British Heart Foundation.