What's the effect on the human body? Do you really know?
Ordinary
atmospheric voltage potential is about 100 V/m near the surface, but it varies quite a bit; near trees and plants it can be several kilovolts per meter. The currents involved tend to be small, on the order of two picoamperes per square meter in free air.
So, we do know that biological systems on Earth deal with ("slowly") changing electric and magnetic fields. We know that some birds use the magnetic fields for navigation, and it looks like some insects like bumblebees and arachnids use these electric fields to detect nearby plants.
The fact that the transmission lines use alternating currents at 50/60 Hz does affect the picture somewhat. Simple measurements show that the effects are very localized to a narrow zone beneath the transmission line (width similar to the height ā or ground-line distance). Observations on plantlife along transmission lines hasn't shown any alarming cellular effects, nor does it seem to negatively affect transient insects. (For example, pollinators do not seem to be adversely affected.) This indicates that there does not seem to be any short term effects; that is, we haven't observed any negative short term effects.
Very strong magnetic fields, however, do have
health concerns, but involve magnetic fields much stronger than those associated with electric power transmission lines. This should not be a surprise, because natural magnetic fields are rather weak compared to natural electric fields.
Many people do not realize that all life on Earth is subjected to all kinds of conditions, including quite a bit of ionizing radiation, including gamma rays (both from space, and from natural radioactive decay). Because biological systems evolve to fit the conditions, it is not at all certain that
removing those actually improves health. For example, there is quite a bit of evidence that because human immune systems have evolved to deal with parasites, the prevalence of allergies in Western countries is actually a result of lessened parasitic load especially in childhood. Because of this, some of those who suffer from life-threatening allergies have sought help from acquiring intestinal parasites; a very controversial topic. (We already know many illnesses that are relatively safe when had as a child, giving a lifelong immunity, but can be very dangerous as an adult.) This means that there definitely is some kind of "boundary" for each stressor beneath which exposure is "safe" and above "not safe", but that boundary varies and depends on other stressors, and thus far our only tool to characterise these is via statistics.
But.. how do you do statistics when the numbers involved are on the same order as people being crushed (injured or died) by tipping vending machines? Or when you have a dozen or more variables affecting each other in a very nonlinear, almost chaotic, manner?
Me, I'm much more worried about the fact that current academic papers' quality is dropping, if we use the fraction of withdrawn or later proven incorrect as a measure of quality. (It's not just a small fraction, but between 25% and 50% on many STEM fields, so is a serious concern.) On top of that, we have media whose best option to remain relevant is to rile people up, via scaremongering and simplification and misunderstandings and, well, clickbait. And this means that anyone doing the kind of statistical analysis I am referring to as necessary to determine what constitutes "dangerous" ā keeping in mind that because we are an intrinsic part of the biome surrounding us,
any change, no matter how "obviously good" you might think it might be, is potentially dangerous; and "no change at all" possibly being even more dangerous (as we've observed that to lead to overspecialization, loss of adaptability, leading to species loss when the environment changes) ā anyone doing that kind of statistical analysis has serious financial and career incentives to well, skew the results to get more publicity.