Laughter is empirically found to be good for your health. For a specific laugh that will increase the length of your life, read David Brooks' column in yesterday's NYTimes.
Brooks goes into the ballistic humor zone about the recent Journal of the American Medical Association article that finds people in the overweight (but not obese) category of BMI body size have exactly the same lifespan as people in the ideal BMI body size.
I've read the article and find it empirically and statistically sound. First rate, in fact.
How do we interpret the article. Combined with other, earlier, good research, your weight in your 30-45 year old period is all that counts. After that, weight doesn't matter much.
BMI body size is given in a table that shows that the average American male at age forty is 5'10 and the average woman is 5'5”. Most people are in the normal and overweight category at this age, but 20% of men and 25% of women are in the obese category and need to loose weight.
Put another way, a male at age 40 can be roughly 5'7” and 175 lbs without any worries. Over 5'7” add five pounds for every inch of height and still be worry free. A woman can be 5'3” and 155 pounds without worries and add five pounds for every additional inch of height and still have a long lifespan.