High cholesterol is accepted by virtually everyone as a passport to a heart attack. Doctors have also suspected that low cholesterol is linked to other dangerous conditions, such as cancer, stroke and liver disease.

But a major new study indicates that cholesterol levels could be one of the great medical red herrings of the century.

Researchers have discovered that neither high or low cholesterol levels seem to have any bearing on the major illnesses, including heart disease and cancer.

The discovery, based on the analysis of 1,954 deaths among a group of 7,000 middle-aged men in Hawaii, all of Japanese descent, could have severe ramifications throughout the health and drug industry.

Researchers from the University of Southern California said that early deaths were caused all the time by other risk factors. They have not discounted the possible link between cholesterol levels and smoking, alcohol and untreated high blood pressure, however. If you do not smoke, drink excessively or suffer from high blood pressure, you do not have to worry about your cholesterol levels, they suggest (JAMA, June 28, 1995).

This may be particularly distressing news for the relatives of those people who committed suicide after deliberately lowering their cholesterol levels to avoid a heart condition.

Research from Italy has confirmed earlier observations that low cholesterol levels tend to make people suicidal. Researchers from the St Anna Hospital in Corso studied the blood levels of 331 people who had attempted suicide, against 331 had not harmed themselves. In virtually all cases, the suicide group had lower levels of cholesterol close to the time they tried to kill themselves (BMJ, June 24, 1995).

If cholesterol is not the problem, perhaps melatonin is. Doctors from the University of Vienna have discovered that people with a heart problem tend to produce lower amounts of the hormone at night. Normally, healthy people release melatonin while sleeping, which tends to stop or slow the activity of the endocrine glands. These glands affect growth and metabolism (The Lancet, 1995; 345: 1408).