All physicians board certified in the XYZ Smart Collagen United States are listed in the American Medical Directory published by the American Medical Association and available in larger libraries. About one fourth of the practicing physicians in the United States are not board certified. This may mean that a doctor failed the exam, never completed training, or is incompetent. It could also mean that the doctor simply has not taken the exam.
As mentioned, the results may be skewed, but it's still worth looking at some possible reasons that explain the numbers. For example, there seems to be a correlation in the study between frequent masturbation and general physical health (as evidenced by the stats regarding working out). One possible explanation could be that some people who masturbate frequently do so because they have a healthy sense of comfort with their sexual being that corresponds with a healthy sense of comfort about their body in general, and which may cause them to want to take steps to keep their body in good physical shape.
Or it could be a "reverse" kind of reason. For example, working out tends to increase testosterone, which in turn tends to increase sex drive. So it may be that the fact that these men are working out frequently encourages them to masturbate frequently.Regular ejaculation (whether via masturbation or partner sex) has been shown to have long term positive consequences in terms of prostate health. And masturbation is a great way to help relieve stress. Stress is a major negative impactor on overall health. Assuming that many men masturbate near bedtime, this can also be a way to ensure a better night's sleep, which has positive health implications as well.
There have been tremendous advances in medicine and healthcare over the last twenty years, affecting everything from our understanding and treatment of certain diseases to the best timing to screen for certain conditions in both men, women and children. Breast cancer, HIV, prostate cancer, Alzheimer's...our ability to identify risk factors and provide early treatment is continually progressing and evolving.