The more a man ejaculates each week, the lower his sperm levels fall, new research shows. However, this ejaculatory frequency only partly explains why a man's sperm count varies widely each time it's checked.

The findings, which appear in the medical journal Fertility and Sterility, are based on a study of 27 healthy men who provided monthly semen samples and responded to questionnaires regarding ejaculatory frequency, duration of abstinence, and episodes of fever. The subjects were followed for 16 months.

No seasonal variations in sperm levels, movement, or shape were seen, lead author Dr. Elisabeth Carlsen and colleagues, from Rigshospitalet in Copenhagen, note. However, ejaculation frequency was higher in spring months than in the winter months.

As noted, sperm levels fell as weekly ejaculatory frequency increased. Compared with one ejaculation, sperm level fell 29 percent with two ejaculations and by 41 percent with three ejaculations. In contrast, ejaculatory frequency seemed to have no effect on sperm movement or shape.

The sperm characteristics noted in one sample often differed greatly from those observed in a subsequent sample from the same subject. This wide variation dropped markedly when three semen samples were used instead of two. Ejaculation frequency, duration of abstinence, and the presence of a fever episode were small contributors to this variation.

"The majority of the (this) variation remained unexplained," the authors note.

The findings also suggest that "at least three semen samples should be recommended to estimate an individual's semen profile," they add.

(Agencies September 2, 2004)