Researchers here process statistical data to suggest that major surgery in later life accelerates cognitive decline. It would be interesting to compare data on serious injuries rather than surgery, as one of the possible mechanisms underlying this effect is a greater presence of senescent cells than would otherwise be the case. Senescent cells produce systemic chronic inflammation, and that is important in the progression of age-related neurodegeneration. Senescent cells are also generated in the course of wound healing, such as recovery from surgery, and some small fraction will always linger, failing to self-destruct or to be cleared from the body by the immune system. Thus we might expect severe injuries and major surgeries to produce some long term consequences to the pace of aging throughout the body. But this is pure speculation; the mechanism could just as well be something else.
Cognitive decline starts before conventional definitions of old age (often 65 years) and accelerates with aging and accumulation of comorbidities. Certain health events, such as stroke, can lead to profound changes in the cognitive trajectory such that there is a permanent "step change" in cognitive function. For 60 years a major concern has been that surgery might also drive long term changes in cognition. Yet studies investigating associations between surgery and long term cognitive outcomes have produced inconsistent results, with reports of cognitive harm, no effect, and cognitive improvement. Despite inconclusive evidence, considerable concern remains about the potential for surgery to induce cognitive impairment. Longer life expectancy implies an increasing number of surgical operations in older adults, hence a better understanding of the extent of any change in cognition after surgery is urgently required.
We use cognitive data from 7532 adults, investigating whether incident major surgical admissions are related to long term changes in the cognitive trajectory, using five waves of cognitive assessments spanning approximately 20 years, with adjustment for major medical admissions. To facilitate interpretation of results, we translate effect estimates to equivalent years of cognitive aging and relate changes to the effect of stroke, an event with an established impact on cognition. We primarily aimed to establish the mean population effect of major surgery on cognitive decline.
After accounting for the age related cognitive trajectory, major surgery was associated with a small additional cognitive decline, equivalent on average to less than five months of aging. In comparison, admissions for medical conditions and stroke were associated with 1.4 and 13 years of aging, respectively. Substantial cognitive decline occurred in 2.5% of participants with no admissions, 5.5% of surgical admissions, and 12.7% of medical admissions. Compared with participants with no major hospital admissions, those with surgical or medical events were more likely to have substantial decline from their predicted trajectory. In conclusion, major surgery is associated with a small, long term change in the average cognitive trajectory that is less profound than for major medical admissions. During informed consent, this information should be weighed against the potential health benefits of surgery.