That is the question. A study in Scotland of 6,000 working men, aged 35 to 64 from West and Central Scotland were tracked for 28 years, and yielded some interesting results. It didn't say, but it appears that a 'unit' is an ounce. According to the article, twenty one units of alcohol per week is the government’s recommended maximum weekly amount.
The results showed that men drinking over 22 units of alcohol a week had a 20% higher rate of admissions into acute care hospitals than non-drinkers, but low levels of alcohol consumption increased the number of days stayed in the hospital.
Those downing 22 or more weekly units had more admissions for respiratory illness, but they had the lowest rates of admission for coronary heart disease. Non-drinkers had the highest rates of admission for coronary heart disease.
The number of admissions for stroke started with a weekly tally of 15 units, and progressively increased the more weekly units were consumed.
Men drinking 22 or more units a week had more admissions for a mental health problem, but non-drinkers had a higher rate of admissions for mental ill health than those who drank between one and 14 units a week. Kind of reaffirms the old adage - all things in moderation.