ADHD and alcohol

This may be a dumb question, but I was wondering if there was any particular reason why so many people with ADHD struggle with alcohol and/or alcohol addiction? I know they can tend to have one or several addictions, but alcohol seems to be one that carries over to quite a few who have ADHD. Is it to quiet the mind? My ADHD husband's sister and brother (brother bi-polar and sister and alcoholic/  bi-polar undiagnosed) both had alcohol addictions. My husband is not ADDICTED to alcohol, but there are times I do think he does drink too much. He can go through a large bottle of heavy liquor (Sambuca) in just a few days, and says he can't get to sleep without a drink. It has worried me at times, especially due to his family's addiction problems. Plus, there are SO MANY other husbands/wives on this forum who ADHD spouses drink way too much. So, I'm asking the question.