The cross-linking theory, also referred to as the glycosylation theory of aging, was proposed by Johan Bjorksten in 1942.
According to this theory, an accumulation of cross-linked proteins damages cells and tissues, slowing down bodily processes resulting in aging.
Recent studies show that cross-linking reactions are involved in the age related changes in the studied proteins.
In this theory it is the binding of glucose (simple sugars) to protein, (a process that occurs under the presence of oxygen) that causes various problems.
Once this binding has occurred the protein becomes impaired and is unable to perform as efficiently.
Living a longer life is going to lead to the increased possibility of oxygen meeting glucose and protein and known cross-linking disorders include senile cataract and the appearance of tough, leathery and yellow skin.