Via Richard Wiseman’s excellent book 59 Seconds: Change Your Life in Under a Minute:

After carefully following the recovery rates of patients who had suffered a heart attack, Friedmann discovered that those who were dog owners, compared to those without a canine pal, were almost nine times more likely to be alive twelve months later. This remarkable result encouraged scientists to explore other possible benefits of canine companionship, resulting in studies showing that dog owners coped well with everyday stress, were relaxed about life, had high self-esteem, and were less likely to be diagnosed with depression.

The same cannot be said for cats. 

And for dogs it's causal, not correlation.

awww... no wonder my life has been so difficult in the past 10 months since my dog died.  :(

Dog owners cope well with everyday stress.

Perhaps one day soon another dog will find you.