In 2003, five per cent of Canadians older than 11 had medically unexplained physical symptoms that could not be definitively identified through physical examination or medical testing.

The symptoms, known as MUPS, are linked to conditions such as chronic fatigue syndrome, fibromyalgia and multiple chemical sensitivity, Statistics Canada reports. Gulf War syndrome is also considered to be a MUPS illness.

The results of the new Health Reports study were released on StatsCan's The Daily news site on Friday.

About 1.2 million Canadians had at least one of the three conditions.

The study found the following key results:

• About 2.4 per cent of the population experienced multiple chemical sensitivity -- a condition in which people develop symptoms upon exposure to synthetic chemicals in doses that usually have no noticeable effect.
• Fibromyalgia was found in 1.5 per cent of the population. People with the condition typically experience pain, lasting three months or more, in at least 11 of 18 specific areas.
• Chronic fatigue syndrome, which is characterized by extreme tiredness, affected 1.3 per cent of Canadians.

Of Canadians who were found to have medically unexplained conditions, 14 per cent experienced at least two of the three listed conditions.

According to the 2003 Canadian Community Health Survey, twice as many women as men experienced each of the three conditions, and the conditions were all more common among Canadians with lower incomes.

And the rate of mental disorder, such as depression or agoraphobia, was higher among people reporting medically unexplained physical symptoms, than among the general population.

Among the subject group, 21 per cent had at least one psychiatric disorder and the rates were highest among those who experienced chronic fatigue syndrome.

By comparison, the rate of psychiatric disorder among people who do not have unexplained symptoms is eight per cent.

The number of people affected by MUPS is also linked to age, the study found. The proportion of people experiencing at least one of the conditions was 1.6 per cent for people between 12 and 24, and peaked at 6.9 per cent for people between the ages 45 and 64.