In the July/August 2025 issue of *Scientific American*, readers shared thoughtful responses and reflections on a range of scientific topics covered in recent articles. These letters to the editor offer personal insights, clarifications, and further scientific context, enriching the ongoing conversations sparked by the magazine’s in-depth reporting.
One reader, Steve Huiting from Nevada City, California, expressed appreciation for Stephanie Pappas’s article “The Truth about Testosterone,” particularly for its cautionary tone about the hormone’s effects. Drawing from his own experience as a transgender man undergoing testosterone therapy, Huiting noted both the positive and challenging aspects of hormone treatment. While he embraced the changes testosterone brought, he recounted an incident in which a misunderstanding led to an accidental increase in dosage. When his testosterone levels rose above 1,000 nanograms per deciliter—exceeding the typical range for cisgender men—he experienced notable side effects such as irritability, impatience, and apathy. The shift altered his social engagement, turning him from an attentive participant in volunteer meetings into someone who felt disconnected and frustrated by others’ opinions. This firsthand perspective highlights the complexity of hormone therapies and reinforces the article’s warnings about dosage and monitoring.
In a response to Max Springer’s “Perfect Slice” article in the Advances section, Dawn Jacobs raised a question about the mathematical problem involving slicing convex shapes. Springer had described the issue as analogous to cutting an avocado into two halves, each revealing a sizeable slice. Jacobs sought clarification on whether “two halves” meant two exact halves or simply two pieces, and whether “some sizable slice” implied that the cross-sectional area of each piece was non-zero, ruling out cuts connected by only a thread. Springer replied that “two halves” refers to two disconnected pieces, not necessarily equal in size. He emphasized that the problem’s core is ensuring that each piece has a cross section of at least a certain minimum area—a nontrivial condition, especially in higher-dimensional spaces. While intuitively straightforward for fruits, the mathematics becomes significantly more intricate as dimensionality increases.
Another intriguing exchange focused on the health benefits of sunlight, sparked by Rowan Jacobsen’s June article “Can Sunlight Cure Disease?” and Martin Picard’s piece “The Social Lives of Mitochondria.” Harold Pupko from Toronto pointed out that Jacobsen’s article left the mechanism of sunlight’s health effects somewhat mysterious, whereas Picard’s work offered clues connecting these benefits to mitochondrial function. Picard and his colleague Nirosha Murugan responded with a detailed explanation of how sunlight interacts with mitochondria at the cellular level. Mitochondria contain chromophores—molecules that absorb specific wavelengths of light—such as cytochrome c oxidase, which is sensitive to red and near-infrared light abundant in sunlight. Absorption of these wavelengths enhances mitochondrial electrochemical potential and ATP (adenosine triphosphate) production, boosting cellular energy.
They cited studies demonstrating that photobiomodulation—exposure to specific light wavelengths—can improve retinal function, reduce Alzheimer’s disease pathology in animal models, and enhance working memory in humans. Notably, a 2024 human study showed that just 15 minutes of exposure to 670-nanometer red light significantly lowered postprandial glucose spikes, underscoring the tangible metabolic benefits of targeted light exposure.
Picard and Murugan also addressed Donald Weller’s curiosity about mitochondria’s role as electromagnetic field sensors or generators. They explained that mitochondria generate some of the strongest electric fields in biology, with voltage potentials across the inner mitochondrial membrane reaching about 30 million volts per meter over nanometer distances. These intense electric fields fluctuate with metabolic activity and could produce low-frequency electromagnetic signals, although current technology cannot yet detect such signals from individual mitochondria. The alignment of mitochondrial inner membranes, known as cristae, at intermitochondrial junctions hints at a collective, socially interactive behavior among mitochondria mediated by electromagnetic phenomena, suggesting an exciting frontier for future research.
In addition to these scientific discussions, readers offered corrections and suggestions for earlier articles. For example, Charles C. Mann’s “Research in Reverse” should have referenced the Canadian National Breast Screening Study, while Clarissa Brincat’s “People Watching” needed to clarify that humans and chimpanzees shared a common ancestor about five million years ago. Additionally, Jyoti Madhusoodanan’s “Prevention Intervention” article should have spelled out OHS