HIGH TESTOSTERONE
I’m grateful for the warnings threaded through Stephanie Pappas’s “The Truth about Testosterone” and would like to elaborate from personal experience. As a transgender man, I adore the effects of testosterone. But I discovered some unwelcome ones when my levels climbed. My higher dosage was accidental; I assumed my doctor wanted me to increase it each week until she said, “Halt!”
It sounds like one man’s accident is another man’s aim, however, given that cisgender men with testosterone in the normal range of 300 to 1,000 nanograms per deciliter (ng/dl) can easily get prescriptions for the hormone. Above 1,000 ng/dl, I grew impatient, irritable and disturbingly apathetic. Once an eager listener at volunteer meetings, I felt like I was the only person in the room. All these other humans with their human opinions! They exasperated me.
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
STEVE HUITING NEVADA CITY, CALIF.
SLICE OF CONFUSION
In “Perfect Slice” [Advances], Max Springer describes a slicing problem involving convex shapes as equivalent to “asking whether an avocado of a given size, no matter the exact shape, can always be split into two halves with each side revealing at least some sizable slice,” in the case of three-dimensional objects.
Does “two halves” mean two true halves or two pieces? And does “some sizable slice” mean that the area of the cut is not zero—that the two “halves” are not connected by just a thread?
DAWN JACOBS VIA E-MAIL
SPRINGER REPLIES: “Two halves” in this problem means two disconnected pieces. Moving your knife completely through a fruit at any angle will always give you two pieces but not necessarily two halves. The description of “some sizable slice” is capturing a deeper mathematical boundary on how large the area of each of the two cross sections will be. As described in my article, the recently proved result of the problem says we can always cut an object into two pieces so that each has a cross section of at least a given size. This may seem intuitive for fruits but gets more complex in higher dimensions.
ILLUMINATING MITOCHONDRIA
“Can Sunlight Cure Disease?,” by Rowan Jacobsen [June], leaves us with a sense of mystery as to the mechanism of action for the health benefits of sunshine. Yet in the same issue, a clue is offered by Martin Picard in “The Social Lives of Mitochondria.” The benefits of sunshine might arise from its effect at the mitochondrial level, as demonstrated in a July Scientific Reports paper by Glen Jeffery of University College London and his colleagues. Picard does recommend diet, socialization and exercise to optimize mitochondrial function, including in a brief reference to his work with Nirosha Murugan of Wilfrid Laurier University in Ontario. But he doesn’t refer to the health benefits of exposure to the outdoors.
HAROLD PUPKO TORONTO
Picard says that, so far, the best hypothesis for how mitochondrial DNA’s inner membrane folds, called cristae, line up appears to involve “electromagnetic fields induced by the flow of electrical charge across” those folds. He then goes on to describe how mitochondria communicate with mitochondria in other cells chemically. Perhaps mitochondria are the field sensors and generators, or possibly the “concentrators,” of biology.
DONALD WELLER HILLSBORO, ORE.
PICARD AND MURUGAN REPLY: Pupko is right that the health benefits of sunshine may act, in part, through mitochondria. To exert biological effects, light must be absorbed by a chromophore. Mitochondria have such chromophores, including cytochrome c oxidase (an electron shuttle in the electron-transport chain), which absorbs red and near-infrared photons, abundant in natural light. These wavelengths enhance the electrochemical potential across the inner mitochondrial membrane, energizing mitochondria and increasing adenosine triphosphate synthesis.
For example, photobiomodulation with near-infrared light can rescue retinal function in vivo and reduce Alzheimer’s pathology in mice. In humans, transcranial photobiomodulation can improve working memory. In a 2024 human study, just 15 minutes of exposure to 670-nanometer red light reduced postprandial glucose spikes by nearly 30 percent.
Mechanistic studies, including simulations and photoacoustic imaging, reveal how different wavelengths of light interact with chromophores. A study using solar simulators that matched the intensity of summer sunlight demonstrated that mitochondrial responses to light are cell-type-specific: epidermal keratinocytes showed mitochondrial damage under intense sunlight, whereas dermal fibroblasts were more resilient. Sunlight can therefore be broadly beneficial, but its effects depend strongly on wavelength, intensity and exposure time, with ultraviolet light carrying well-known risks.
Mitochondria’s broader light sensitivity may also help explain why time spent in nature feels restorative. Plants reflect much of the near-infrared spectrum, saturating green spaces with low-energy, tissue-penetrating wavelengths.
In response to Weller: Across biology, mitochondria produce some of the strongest electric fields. As food-derived electrons flow toward oxygen, the electron transport chain generates an electrochemical gradient across the inner mitochondrial membrane. The voltage potential spans a distance of only about five nanometers, producing an electric field on the order of 30 million volts per meter.
These immense electric fields rise and fall with metabolic demands and energy flow. Such fluctuations in electric fields are expected to generate low-frequency electromagnetic signals. Although it is beyond the reach of today’s instruments, detecting such signals from individual mitochondria appears to be an essential step toward fully understanding them as a social, energetic collective that transforms and regulates energy across living systems. And the composition of mitochondria suggests they may not only generate but also respond to electromagnetic fields.
Perhaps the best direct evidence of biologically relevant fields at the scale of mitochondria is the transmitochondrial cristae alignment. This occurs at intermitochondrial junctions, electron-dense contacts between two mitochondria.
ERRATA
“Research in Reverse,” by Charles C. Mann [September], should have referred to the Canadian National Breast Screening Study of cancer.
“People Watching,” by Clarissa Brincat [Advances; October], should have quoted Laura Lewis as saying that humans’ and chimpanzees’ shared primate ancestor lived around five million years ago.
In “Prevention Intervention,” by Jyoti Madhusoodanan [Innovations in Alzheimer’s; October], OHSU’s name should be Oregon Health & Science University.
