How much exercise is 'enough'?
This could be the shortest blog post ever:
Doing even a small amount of exercise is better than doing none
Doing more exercise is almost always better
There. Sorted.

Oh - you wanted me to go into a bit more detail? Well, since you asked.
You will hear a variety of mixed and sometimes conflicting messages about how much exercise is 'enough'. The source of these conflicts is often down to how public health experts try to tackle the current inactivity crisis. According to a report by the WHO, 3.2 million deaths a year are due to insufficient exercise. Around 50% of women and 40% of men in the US and Europe not being almost totally sedentary. So, to improve the overall health of the whole population, getting inactive people to do even the smallest amount of exercise would have a significant impact.
Even being just a little bit active (but without meeting national exercise guidelines) helps reduce the chance of you dying by 30%. By doing moderate exercise, that increases to 38% and intense exercise takes the reduction to 50%! So 30 minutes of intense exercise, five times a week, cuts your risk of dying from ALL CAUSES by half! Which is great. But is there any benefit to doing more than the Government guidelines?
Definitely.
A huge study was done in the US involving 120,000 runners since 1991 and it clearly showed that the more exercise you do, and the harder you do it, the more benefits you get from it. You will lower the risk of dying from diabetes, stroke and heart attack. But you will also lower the risk of getting glaucoma, cataracts and macular degeneration - by up to 70% if you do more than 30 minutes of exercise, five times a week.
And you can continue to benefit, by adding more miles (reducing your risk of glaucoma by 8% per extra mile), or running faster (for every additional metre per second you add to your speed, you reduce your heart attack risk by 50%).
It's at this point I should say that if you don't fuel your exercise properly, and don't make sure you get a good night's sleep, then excessive intense exercise will reduce your immune system, and it's also possible to overtrain - but these are often short-term and can be easily reversed by having a sensible diet and taking regular rest days.