I guess I’ve left it too late to have a mid-life crisis – I’d have to live to beyond 120, even if it started today – and even with the most up-to-date modern technology, I don’t think I’ll make it to that. Interestingly, over lunch today, I was talking with Sam, my eldest son, about stress and life span. Do stressed people, he asked, or for that matter, stressed animals, live shorter lives than unstressed ones?
Such a question is really difficult to answer due to all the factors involved in living with socioeconomic stress, which is associated with lower longevity. So, which are associated with an earlier death? Even if we could work that out, association doesn’t equal causation, as we are so regularly told.
Such a question is really difficult to answer due to all the factors involved in living with socioeconomic stress, which is associated with lower longevity
A quick literature search shows some fascinating studies, though. Fibroblasts taken from animals subject to psychosocial stress have a shorter lifespan in cell culture. On the other hand, animals showing resistance to similar stressors have a longer lifespan, as do their cells in culture. Molecules protecting from stress at a macro- or a micro-level, such as heat shock proteins, are upregulated in animals coping with the stress they endure, while animals that fail to cope don’t show elevation in these chaperone proteins.
“Has this any relevance to people or their pets?”, I hear you ask. Well, individuals who regularly participate in cold water swimming are generally healthier. However, whether it is healthier people who undertake such exercise or the cold water that makes the difference might be questioned.
Rats exposed to cold water lived significantly longer (968 days versus 923 for rats not exposed to such cold) and had fewer tumours (24 percent of cold-exposed rats having malignancies rather than 57 percent in control animals) (Holloszy and Smith, 1986). But the rats did tend to develop a cold nephropathy and die of kidney failure, though at an advanced age. Therefore, we might ask whether human populations living in cold environments have a greater lifespan than those in warm climates. Sadly, the significant economic factors in Inuit populations, for example, have much greater influence than environmental influences, rendering such questions unanswerable.
We might ask whether human populations living in cold environments have a greater lifespan than those in warm climates
Maybe there are factors that are easier to investigate. Caloric restriction acts significantly in rodents to increase lifespan – this was shown as far back as 1935 by Clive McCay in a seminal paper (McCay et al., 1935). Does this have any relevance to humans, though?
Luigi Cornaro, a wealthy Venetian nobleman in the 1490s, indulged in a life of excess until middle age when his health began to fail to the point that he thought he was about to die. On medical advice, he took up a calorie-restricted diet, eating only a few hundred grams of food daily. He lived to 102, writing his results in a book entitled Discourse on a Sober Life. My dear friend Mary Brancker, the first female president of the BVA, who qualified from the RVC in 1937, said that with the Depression after the First World War, then the Second World War and rationing after that, she didn’t stop feeling hungry until she was in her late 30s. She lived till she was 97.
We are told, though, that data is not the plural of anecdote. So, have we got evidence from larger populations? How could we experiment on people in the way and extent it is possible with rodents?
In the early 1990s, a remarkable experiment, Biosphere 2, encapsulated eight scientists in a three-acre, 7 million cubic foot ecological dome for two years, with a variety of ecological biomes and some pygmy goats for milk and chickens for eggs. Without meaning to evaluate caloric restriction, they found that, as they could only eat what they produced, they ended up consuming a low-calorie (1750 to 2100 kcal/d) nutrient-dense diet of vegetables, fruit and nuts, with only a small amount of supplemental meat protein. After two years, the crew members’ body mass index had, understandably, reduced markedly, as had blood pressure, cholesterol, leucocyte count and a number of other physiological variables, just as occurs in calorically restricted rodents. The crew members were in excellent health only having had, between them, five days off from their strenuous workload through the entire two years.
We started off today talking about stress and longevity, didn’t we? I guess the real amazement with the whole Biosphere 2 project is not that the project worked from an ecological perspective, though that is remarkable and shows how well the scientists involved had calculated the bioenergetics. It’s that the crew lived together so cohesively and harmoniously through the entirety of the project. Talking afterwards, they said that they realised any disagreement or falling out could endanger their health and the project altogether.
I have a nasty suspicion that we have not learned its key lesson – that the entirety of the human population of the biosphere needs to work together to keep the world as a whole from collapsing
Sadly, a second attempt to run the project collapsed not because of problems on the inside but because of financial mismanagement on the outside. The aim of Biosphere 2 was to act as a research and educational warning of the perils facing Biosphere 1 – the earth. I have a nasty suspicion that we have not learned its key lesson – that the entirety of the human population of the biosphere needs to work together to keep the world as a whole from collapsing. Oh my – I hadn’t expected this to end on such a sour note. Hopefully, in 2024, we can aim for better and learn those lessons – happy new year!