This paper summarizes a symposium that has shown that sleep is a state of altered metabolism, and that disturbances and curtailments of sleep have far-reaching effects on endocrinology, immunology and metabolism, changes that may be linked to disease. As yet, the entire causal chain is weak but there are indications that, in particular, the risk of type 2 diabetes and cardiovascular disease may result from disturbed sleep. It is hypothesized that both insulin resistance and chronic low-grade inflammation may be involved.