Found a reference on LIVESCIENCE to a Danish study (2015) on the health benefits of moderate running 3 times a week - thought others may be interested. Here is the link
livescience.com/49667-joggi...
Here is a summary quote from the article:- (if that's allowed?)
"The best outcomes in the study were associated with running between 1 and 2.4 hours per week, with no more than three days of running per week, at an average or slow pace. "Many adults will perceive this to be a goal that is practical, achievable and sustainable," the researchers said. "
I won't worry that I can only cover 4km in 30 minutes now!!