I believe "may" is the operative term. May cause health disorders. This is not absolute, and it is ridiculous for anyone to conclude otherwise. Of course, we are all entitled to our opinions: some parents believe in spanking, some don't, Personally, it seems reasonable to presume that many other factors, in addition to spanking, contribute to a child's mental health. Such behaviours as screaming wildly or employing verbal abuse when disciplining the child (i.e. name calling) may also be damaging, as it exemplifies poor control, impacts self-esteem, and can seriously impede a child's ability to manage conflict in constructive ways. Failing to correct children for their wrongdoing (as so many parents appear to do these days) is also damaging, for it can produce spoiled brats and, inevitably, self-entitled adults. (If there must be a study, try that for a subject!)

The fact is, children can be abused or poorly raised with or without spanking. My bottom was firmly swatted (each time had it coming!), and there is nothing wrong with me; I am not violent in the least and I rarely drink. I have friends who were not spanked, and, likewise, there is nothing wrong with them. I know people who were spanked or beaten and today bear the emotional scars. I know people who, seemingly, were never disciplined in any way, and they are dreadful to have around. So, what can be concluded from this? I may only answer from personal experience: Parenting, however it is done, can make or break a child. It is not one single act, but many things that play a part. I had strong, supportive parents who punished me. Yet I was never put down. I was never pushed or physically injured or made to feel badly about myself. I was not abused in any way. Spanking was balanced with love. I knew what naughtiness would bring; but I also KNEW my parents loved me.

To be sure, spanking can be abusive. However, so may a lot of other disciplinary forms: in the case of child abuse, it is usually a combination of detrimental parenting methods and/or a turbulent home life that creates an emotionally unhealthy environment for children. It may be hard for some to fathom, but there are, indeed, parents with sense enough to know the difference. Mine did.

Children should have a right to their bodies, and the right to say "No!"

Currently in the U.S.:

When an adult does it to another adult, its sexual battery:
http://hamptonroads.com/2011/12/va-beach-restaurateur-pleads-guilty-sexual-battery

When children do it to adults, its a "deviant sexual prank":
http://www.theday.com/article/20101207/NWS04/101209750

When an adult does it to a person under the age of 18, its "good discipline".

Research/recommended reading:

Spanking Can Make Children More Aggressive Later
http://tulane.edu/news/releases/pr_03122010.cfm

Spanking Kids Increases Risk of Sexual Problems
http://www.unh.edu/news/cj_nr/2008/feb/lw28spanking.cfm

Use of Spanking for 3-Year-Old Children and Associated Intimate Partner Aggression or Violence
http://pediatrics.aappublications.org/cgi/content/abstract/126/3/415

Spanking Children Can Lower IQ
http://www.unh.edu/news/cj_nr/2009/sept/lw25straus.cfm

Plain Talk About Spanking
by Jordan Riak
http://www.nospank.net/pt2010.pdf

The Sexual Dangers of Spanking Children
by Tom Johnson
http://nospank.net/sdsc2.pdf

"Spanking" can be intentional or unintentional sexual abuse
http://www.nospank.net/101.htm