What is stress? The engineer in me is tempted to use the precise definition: “the pressure or tension exerted on a material object” with its counterpart strain being the magnitude of the change in dimension of the material object in response to the stress. In people terms, then, stress is something external to ourselves, and strain would be how we deal with the stress. But of course, being human, we’ve reversed the meanings, so we might say, “I’m under a lot of strain right now, and I’m feeling very stressed”!
However, for this essay, I want to talk about stressors as things external to ourselves that can have either good or bad effects on us. Environmental things like heat or cold; chemical exposures both internal and external; radiation including from the sun, and mechanical effects such as from exercise.
An important principle that determines whether a stressor will have a good effect or a bad effect is hormesis, the idea that an organism’s response to a stressor is based on dose. So at usual doses, something might not even be considered a stressor! Water, oxygen, and sunlight are three examples. We don’t think of them as stressors, but clearly, at very low doses we will experience distress, while at very high doses all three cause major problems (water intoxication kills marathon runners; too much oxygen causes blindness in premature infants; overexposure to sunlight results in burns and cancers).
Physical exercise consists of applying a stressor to muscles, ie causing a muscle to contract against response. At appropriate doses (muscle loads) this causes microtears which stimulate muscle growth as part of the healing process. Too high a load can cause ruptures of muscles or tendons, however. Similarly, bones become stronger when subjected to stretching forces from muscles and ligaments (weight-bearing exercise). Again, too high a load results in bone fractures. And lack of exercise results in weakening of both muscle and bone! And, although it’s not the point I want to make here, increasing protein, calcium, or vitamin D intake has no effect on muscle or bone strength without exercise!
The hormesis principle seems to apply to just about anything that affects us. It may explain why the high doses of vitamins, antioxidants, or minerals provided by supplements fail to be helpful, compared to the moderate doses when these substances are obtained in whole foods.
We might also want to take hormesis into account when assessing environmental risks. Background ionizing radiation, for example from cosmic rays or radon gas in soil, is usually considered bad for our health according to the Linear No-Threshold model (LNT) which predicts that even low doses can cause cancer and that the risk increases linearly with dose and with cumulative dose over time. However, the LNT model fails to take into account the DNA repair and programmed cell death mechanisms built into every cell, and is contradicted by findings that low doses of background radiation actually increase healthy longevity, in what appears to be a hormetic effect.
Environmental toxins such as arsenic, cadmium, or agricultural pesticides may also manifest hormesis, with low doses actually being beneficial to the organism1.
In this essay, I’ve talked about the anti-inflammatory effects of various interventions, such as caloric restriction, protein restriction, methionine restriction, exercise, curcumin, resveratrol… Hormesis applies to all of them, and also to what I believe to be the underlying common mechanism, insulin.
So a general principle is that stressors at low doses can improve your health. That means that we needn’t worry so much about avoiding potentially dangerous things in our environment. Do we need to be so fastidious about washing produce to get rid of agricultural pesticide residues, when it’s been demonstrated that low doses of paraquat increase lifespan in C. Elegans worms2? Fastidiousness about dust, dirt, and pet hair in general may also be misplaced; see this article by Joe Schwarcz of McGill University’s Office for Science and Society.
In an earlier instalment, I suggested that vitamin D supplements might be helpful because we’ve become so frightened of exposing our skin to the sun (the best method for getting vitamin D) that we avoid going out, we cover our skin, and we use high-SPF sunblockers. Is it possible that we might be overdoing it? Avoiding sun exposure may have negative effects; for example, living in areas with more ultraviolet light exposure was associated with reduced risk of estrogen-receptor-negative breast cancer, but this association disappeared for women regularly taking vitamin D supplements3. And while it is known that UV exposure through sunlight to the retina might contribute to increased retinoblastoma incidence, it is possible that sun exposure in early childhood protects against retinoblastoma4.
Besides sun exposure, there are other powerful influences on the risk of skin cancer. In women, environmental exposure to PCBs (Polychlorinated Biphenyls) and organochlorine pesticides significantly increased risk of cutaneous malignant melanoma5. And it’s not just sun exposure, it’s risky behaviour such as tanning beds and getting sunburns that are important.
Personally, I aim to maximize sun exposure (for both vitamin D and to promote tanning) but stop well short of sunburn. So if I go for a long bicycle ride, I will apply a fairly low SPF sunscreen to the most exposed skin, and take along the sunscreen in case I am out for longer than planned. The more tanned I become, the longer I can be out without risking sunburn.
So, just to repeat my message that stressors at low doses may be good for your health, I should mention that studies have revealed animal performance benefits in response to stressful changes in oxygen, temperature, ionizing radiation, heavy metals, pesticides, dehydration, gravity, and crowding6.
Personally, I suspect that the beneficial health effects of some commonly prescribed medications may be because they are stressors. In instalment 9, I provided a link to my review of the book “Deadly medicines and organized crime: how big pharma has corrupted healthcare,” by Dr. Peter Gøtzsche. In that review, I go into some detail on the lack of evidence that antihypertensive medications improve outcomes because of blood pressure lowering, or that statins improve outcomes because of cholesterol lowering. Could they actually work because they are stressors (as evidenced by side effects!)?
In the next (and final) instalment, I will tell you about what I personally look for at the grocery store, and what I like to cook. And if there is room, I want to share a bit of what I’ve learned about gout, which is a bit of a special case when it comes to inflammation.
Until then, don’t stress about stress!
- Lajqi T, Stojiljkovic M, Wetzker R. Toxin-induced hormesis may restrain aging. Biogerontology. 2019;20:571-581. PMID 30895414 ↩
- Yang W, Hekimi S. A mitochondrial superoxide signal triggers increased longevity in Caenorhabditis elegans. PLoS Biol. 2010;8:e1000556. PMID 21151885 ↩
- Gregoire AM, VoPham T, Laden F et al. Residential ultraviolet radiation and breast cancer risk in a large prospective cohort. Environ Int. 2021;159:107028. PMID 34894486 ↩
- Orjuela-Grimm M, Carreño SB, Liu X et al. Sunlight exposure in infancy decreases risk of sporadic retinoblastoma, extent of intraocular disease. Cancer Rep (Hoboken). 2021;4:e1409. PMID 33960746 ↩
- Darvishian M, Bhatti P, Gaudreau É et al. Persistent organic pollutants and risk of cutaneous malignant melanoma among women. Cancer Rep (Hoboken). 2021e1536. PMID 34414694 ↩
- Berry R, López-Martínez G. A dose of experimental hormesis: When mild stress protects and improves animal performance. Comp Biochem Physiol A Mol Integr Physiol. 2020;242:110658. PMID 31954863 ↩
- instalment 10: more prescription medications that may be helpful in certain situations
- instalment 12: my grocery shopping list