Keywords: biological clock, disturbed day-night rhythm, muscle metabolism, stress hormone

Many of the processes of the human body are affected by the biological clock and follow a day-night rhythm. It is suggested that a disturbed day-night rhythm (due to jet lag or shift work, for instance) has negative health effects. The results of this dissertation show that human muscle metabolism follows a day-night rhythm. They also indicate that a disturbed day-night rhythm is associated with lower insulin sensitivity (which may lead to diabetes mellitus). This dissertation also focusses on the impact of a common genetic variation of the stress hormone receptor (the Bcll polymorphism). It is shown that people with one of the Bcll polymorphism variants are likely to have higher weight, higher average blood pressure levels and a greater extent of arteriosclerosis.