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Men’s testosterone levels dropping, study says

Nov. 4, 2006
Special to World Science  

The past two decades have seen a “sub­stan­tial” and un­ex­plained de­crease in Amer­i­can men’s tes­tos­ter­one lev­els, a study has found.

Tes­tos­ter­one is a po­tent “male” hor­mone pro­duced chief­ly by the tes­tes, and chief­ly re­spon­si­ble for the de­vel­op­ment of male sex­u­al char­ac­ter­is­tics. The sub­stance al­so strength­ens mus­cle tone and bone mass, and pro­motes good health in men. 

The down­ward trend seems to be “due to some un­doc­u­ment­ed his­tor­i­cal or con­tem­po­rary in­flu­ence, health-related or en­vi­ron­men­tal,” wrote re­search­ers with the New Eng­land Re­search In­sti­tutes in Wa­ter­town, Mass., in the stu­dy.

The find­ings ap­pear in the ear­ly on­line edi­tion of the Jour­nal of Clin­i­cal En­do­cri­nol­ogy and Me­tab­o­lism.

Av­er­age lev­els of the hor­mone dropped by 1 per­cent a year, the re­search­ers re­ported. While a man’s tes­tos­ter­one lev­el typ­i­cal­ly falls stead­i­ly with age, the in­ves­ti­ga­tors found what they ar­gued was a faster de­cline than could be at­trib­ut­ed to ag­ing alone.

They sug­gested that rising obes­i­ty rates and de­cline in smok­ing might par­tially ex­plain the find­ings, since both fac­tors are as­so­ci­at­ed with low­er tes­tos­ter­one lev­els. But these trends ac­counted for on­ly a small per­centage of the drop, they added.

The re­search­ers said the study pop­u­la­tion was rel­a­tively lim­it­ed, con­sist­ing of 1,532 men from the great­er Bos­ton ar­e­a, and thus the re­sults need to be con­firmed by fol­low­up re­search.


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The past two decades have seen a “substantial” and unexplained decrease in American men’s testosterone levels, a study has found. Testosterone is a potent “male” hormone produced chiefly by the testes, and chiefly responsible for the development of male sexual characteristics. The substance also strengthens muscle tone and bone mass, and promotes good health in men. The downward trend seems to be “due to some undocumented historical or contemporary influence, health-related or environmental,” wrote researchers with the New England Research Institutes in Watertown, Mass., in the study. The findings appear in the early online edition of the Journal of Clinical Endocrinology and Metabolism. Average levels of the hormone dropped by 1 percent a year, the researchers reported. While a man’s testosterone level typically falls steadily with age, the investigators found what they argued was a faster decline than could be attributed to aging alone. They suggested that a spread in obesity rates and decline in smoking might partially explain the findings, since both factors are associated with lower testosterone levels. But these trends accounted for only a small percentage of the drop, they added. The researchers said the study population was relatively limited, consisting of 1,532 men from the greater Boston area, and thus the results need to be confirmed by followup research.