Per bone density above. Nothing going for walk regularly won’t solve. Low bone density generally means you’ve been sedentary when off the bike. Plus walking will avoid many the common injuries you hear your running mates complaining of.
The above is true, just as Confused above is correct.
Way back in the 80's I got into running through lunchtime runs at work, where there were a few club runners. I graduated through the slower groups to the faster group and got into road and cross-country running, completing 5 marathons in the process as well as many 1/2 marathons and shorter races. As I neared my 40's I decided that pounding the roads was not doing my knees any good and decided to take up triathlon, which got me cycling and reduced the running miles. While my swimming was no better than competent and the cycling was all effort and no technique, on the run section, though, I was enjoying passing lots of better swimmers and cyclists. The cross-training was a huge benefit and the year I turned 40 I ran a lot of pb's in club races.
A couple of years later and I burst a hamstring badly playing football and my running, once I was able, went from sub 6-minute miles to more like 7:30 minute miles and never recovered. I don't/can't run now - having stopped for a long time, I tried to start again and my achilles complained in a major way.
There's no doubt in my mind combining running and cycling is good for your fitness and a good way of maintaining bone density. I note that Beth Potter, an Olympic 10k runner in Rio, is now GB's top female triathlete, winning at Euro level fairly recently. The top triathletes are very good runners - running 10k's at close to 30 minutes pace, after the swim and cycle, is a pretty good standard.
These days I play golf several days a week to get my weight-bearing exercise and cycle. I think I'm still pretty fit for my age.