This conclusion originates from more than ten epidemiological studies made mainly among industrial workers. Chronic tiredness, nervousness and low spirits are also more common among shift workers than in other employee groups. However, there is no evidence that shift work causes a higher risk of serious mental illnesses such as depression. Increasing age means lower body adaptability to night work. While the first night shows no age-related differences, in subsequent consecutive night shifts older workers get tired more easily than their younger workmates.
Lack of sleep is twice as common among working people than among the unemployed and pensioners.
Tiredness, naturally, results in impaired job performance. Shift work also has a negative impact on the reproductive health of women. The menstrual period becomes more irregular and fertility decreases. The mental power of deduction and the ability to perform mental arithmetic decrease after the first eight hours of work. This is the common experience of working men and women common all over the world.