steak tacos

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3 of 5
Decade: 40s

What to do: More exercise—any kind will do
Why: It'll help protect your telomeres, the stretches of DNA on the ends of our chromosomes that get shorter with age and leave cells vulnerable to damage. In a study in Medicine & Science in Sports & Exercise, the more physically active people were during middle age, the lower their risk for shortened telomere length and the healthier their cells stayed as they aged.
The Plan: Focus on the 4 activities tracked in the study: weight training, moderate cardio like jogging, vigorous cardio like Spinning or a trendy rowing class and walking or biking.