Working long hours was not necessary in those days, it was forced upon people by declining wages as profit was transferred from individuals, families, and small businesses towards the capital class. The entire movement to introduce the 40 hour work week was based on people wanting to reduce their hours towards what their grandparents worked and survived on. The entire luddite movement was based on declining wages and worsening work conditions compared to the generations before them.
I don't know where you're getting that information from, but analysis of the bones of American colonists shows they worked themselves to an early death.
Life expectancy and average height improved throughout the 19th century.
