While optimal weekly running mileage depends on your individual situation (medical history, etc.), the 20-year National Runners Health Survey of more than 100,000 runners is one about which you may want to know.

Conducted by Dr. Paul Williams – staff scientist at the Lawrence Berkeley National Laboratory in Berkeley California – the survey found that the optimal number of miles to run a week is almost twice that recommended by those in the public health field. While public health officials recommend about 3.5 hours (fewer than 20 miles per week) Williams’ study found greater health benefits for runners logging up to 49 miles a week. (Similar benefits, the survey maintains, would be gained from increased workouts in other aerobic sports.)

Here are a few highlights of the survey:

To beat the weight gain battle in middle age, runners need to increase their mileage by about 1.4 miles a week annually.

Increasing weekly mileage from 20 to 40 miles per week may reduce the risks of stroke by 69%, coronary heart disease by 37% and diabetes by 68%.

Exercise intensity is associated with greater reductions in blood pressure and other cardiac risks.

Here’s the link for more details.