Over the last few years, a movement has grown where followers are spending thousands of dollars on rigorous and sometimes extreme health practices with the goal of extending their lives. The leaders of the “longevity” movement reach their mostly male audience largely through YouTube and podcasts.

Longevity has become a major wellness industry, with big money involved. But critics say the science behind it is often unfounded and misleading. The Globe’s demographics reporter Ann Hui spoke to the men who practice longevity, those who preach it, and those who criticize it.

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