In mice, certain genes seem to link being heavier early in life to a shorter life, especially in males — but being heavier later in life is actually linked to living longer, showing that the effect of weight on lifespan changes with age and sex.

In mice with different genes, scientists found 29 specific gene spots that affect how long they live — but these genes act differently depending on whether the mouse is young or old, and whether it's male or female. Some genes only matter at certain life stages, and some even switch from helping to hurting (or vice versa) as the mouse ages.

In mice, the genes that affect how long they live work differently in males and females — many of the gene interactions are totally separate between the sexes.

In male mice, being heavier as a young adult is linked to a shorter life — each extra gram might take away up to 14 days. This effect is much stronger in males than in females, suggesting their genes handle weight and aging differently.