Readers Respond — Testosterone Risks, a Geometric Slice, and Sunlight’s Mitochondrial Link

Readers write in about several pieces from our July/August 2025 issue. The letters touch on testosterone therapy, a mathematical slicing problem, and how sunlight might influence mitochondria. Below we publish the readers' accounts and authors' replies, revised for clarity and context.

On testosterone

One reader, a transgender man, writes in about Stephanie Pappas’s feature “The Truth about Testosterone.” He welcomes many of testosterone’s effects but describes an accidental dosage increase that raised his blood level above about 1,000 ng/dl. At that level he reports marked impatience, irritability and unusual apathy: activities that previously engaged him—such as listening attentively at volunteer meetings—felt intolerable.

STEVE HUITING, Nevada City, Calif.

His account underscores the importance of careful medical supervision when adjusting hormone therapy. Clinicians typically monitor symptoms and blood levels to balance benefits and side effects; anyone experiencing mood changes or other concerning effects should consult their provider promptly.

On slicing convex shapes

A reader asked for clarification of Max Springer’s “Perfect Slice” [Advances], which likened a geometric problem for convex bodies to asking whether an avocado of a given size can always be sliced so that each side reveals a substantial cross section.

DAWN JACOBS

Springer replies: In this mathematical context, “two halves” means two disconnected pieces, not necessarily equal-volume halves. Any full cut through a solid produces two pieces, but the theorem of interest guarantees a quantitative lower bound on the cross-sectional area of each resulting piece—a guarantee that becomes subtler when generalized to higher dimensions.

On sunlight and mitochondria

A reader who found Rowan Jacobsen’s “Can Sunlight Cure Disease?” puzzling points to Martin Picard’s “The Social Lives of Mitochondria” as suggesting a mechanism: light acting on mitochondria. Other correspondents expanded on that idea, noting recent experimental work and theoretical possibilities.

HAROLD PUPKO, Toronto

Picard and Nirosha Murugan reply: Sunlight can produce biological effects when photons are absorbed by chromophores. Mitochondria contain chromophores—most notably cytochrome c oxidase in the electron-transport chain—that absorb red and near-infrared light. Those wavelengths can enhance the electrochemical potential across the inner mitochondrial membrane and increase ATP production, a process sometimes termed photobiomodulation.

Evidence cited includes animal studies in which near‑infrared light rescued retinal function and reduced Alzheimer’s-type pathology, and human studies of transcranial photobiomodulation that report improvements in working memory. They also reference a 2024 human study in which 15 minutes of exposure to 670-nanometer red light was associated with an approximately 30% reduction in postprandial glucose spikes. Mechanistic work—simulations and photoacoustic imaging—helps map how different wavelengths interact with chromophores.

Picard and Murugan also note that responses are cell-type-specific: in solar-simulator experiments that approximate intense summer sunlight, epidermal keratinocytes showed mitochondrial damage while dermal fibroblasts were more resilient. Thus the net health effects of sunlight depend strongly on wavelength, intensity and duration; ultraviolet wavelengths retain well-established risks.

On the idea that mitochondria generate biologically meaningful fields: the inner mitochondrial membrane supports a large voltage across a short distance (on the order of five nanometers), giving rise to very large local electric fields—estimates often cited are on the order of 10^7 to 10^8 volts per meter. These fields fluctuate with metabolic activity and could produce low-frequency electromagnetic signals in principle, though detecting such signals from individual mitochondria remains beyond current experimental reach. Structural phenomena such as cristae alignment at intermitochondrial junctions provide intriguing candidates for field-mediated organization but require further study.

Corrections and clarifications

• Charles C. Mann’s “Research in Reverse” (September) should have cited the Canadian National Breast Screening Study.
• Clarissa Brincat’s “People Watching” [Advances; October] should have attributed to Laura Lewis the estimate that the human–chimpanzee common ancestor lived roughly five million years ago.
• Jyoti Madhusoodanan’s “Prevention Intervention” [Innovations in Alzheimer’s; October] should have expanded OHSU to Oregon Health & Science University.

Note: We have preserved the readers’ perspectives and the authors’ replies while clarifying technical points and emphasizing the need for clinical oversight where medical topics are concerned.