It is held in many mental health circles that masturbation can relieve depression and lead to a higher sense of self-esteem. Masturbation can also be particularly useful in relationships where one partner wants more sex than the other – in which case masturbation provides a balancing effect and thus a more harmonious relationship. Mutual masturbation, the act by which two or more partners stimulate themselves in the presence of each other, allows a couple to reveal the "map to [their] pleasure centers". By watching a partner masturbate, one finds out the methods they use to please him- or herself, allowing each partner to learn exactly how the other enjoys being touched. Intercourse, by itself, is often inconvenient or impractical at times to provide sufficient sexual release for many people. Mutual masturbation allows couples to enjoy each other and obtain sexual release as often as they need but without the inconveniences and risks associated with sex. In 2003, an Australian research team led by Graham Giles of The Cancer Council Australia found that males masturbating frequently had a lower probability to develop prostate cancer. Men who averaged five or more ejaculations weekly in their 20s had significantly lower risk. However they could not show a direct causation. The study also indicated that increased ejaculation through masturbation rather than intercourse would be more helpful as intercourse is associated with diseases (STDs) that may increase the risk of cancer instead. However, this benefit may be age related. A 2008 study concluded that frequent ejaculation between the ages of 20 and 40 may be correlated with higher risk of developing prostate cancer. On the other hand, frequent ejaculation in one's 50s was found to be correlated with a lower such risk in this same study. A study published in 1997 found an inverse association between death from coronary heart disease and frequency of orgasm even given the risk that myocardial ischaemia and myocardial infarction can be triggered by sexual activity. The association between frequency of orgasm and all cause mortality was also examined using the midpoint of each response category recorded as number of orgasms per year. The age adjusted odds ratio for an increase of 100 orgasms per year was 0.64 (0.44 to 0.95). That is, a difference in mortality appeared between any two subjects when one subject ejaculated at around two times per week more than the other. Assuming a broad range average of between 3 to 5 ejaculations per week for healthy males, this would mean 5 to 7 ejaculations per week. This is consistent with a 2003 Australia article on the benefits against prostate cancer. The strength of these correlations increased with increasing frequency of ejaculation. A 2008 study at Tabriz Medical University found ejaculation reduces swollen nasal blood vessels, freeing the airway for normal breathing. The mechanism is through stimulation of the sympathetic nervous system and is long lasting. The study author suggests "It can be done [from] time-to-time to alleviate the congestion and the patient can adjust the number of intercourses or masturbations depending on the severity of the symptoms." Masturbation is also seen as a sexual technique that protects individuals from the risk of contracting sexually transmitted diseases. Support for such a view, and for making it part of the American sex education curriculum, led to the dismissal of US Surgeon General Joycelyn Elders during the Clinton administration. EU Nations include masturbation in their sex education and promote the practice. Sexual climax, from masturbation or otherwise, leaves one in a relaxed and contented state. This is frequently followed closely by drowsiness and sleep – particularly when one masturbates in bed.Some professionals consider masturbation to function as a cardiovascular workout.Though research is still as yet scant, those suffering from cardiovascular disorders (particularly those recovering from myocardial infarction, or heart attacks) should resume physical activity (including sexual intercourse and masturbation) gradually and with the frequency and rigor which their physical status will allow. This limitation can serve as encouragement to follow through with physical therapy sessions to help improve endurance.