Going under general anesthesia probably won’t raise your risk of brain fog, new research suggests.

Published Wednesday in Mayo Clinic Proceedings, study authors examined the medical records of 1,731 elderly yet cognitively healthy people living in Olmsted County, Minn., and found there was no substantial link between cumulative anesthesia exposure after the age of 40 and later mild cognitive impairment (MCI). In certain circumstances, however, particularly for those who were given general anesthesia after 60 and underwent non-bypass (vascular) heart surgery, there did appear to be a slight association between the two events, indicating the story might be a bit more complicated than it appears.

"We looked at a group of patients who have been followed here in Olmsted County, where we have detailed information about their cognitive function as they age,” explained senior author Dr. David O. Warner, an anesthesiologist at the Mayo Clinic, in a statement. “The bottom line of our study is that we did not find an association between exposure to anesthesia for surgery and the development of mild cognitive impairment in these patients."

For some time now, there have been speculative, if not entirely unfounded worries that the use of anesthesia, even once, can trigger long term effects on the human brain — especially dementia among the elderly. It’s already known that some people who go under experience a temporary daze, or transient cognitive dysfunction, afterwards; this risk increases in the elderly. As Warner and his colleagues note though, it’s difficult for studies to separate out the coexisting risk factors for dementia that come alongside anesthesia use, such as underlying health conditions or the bodily stress of going through major surgery itself. Likewise, because dementia often takes years to develop, finding a concrete connection is harder.

To remedy some of these complications, the researchers decided to focus on mild cognitive impairment, described by them as a “stage of cognitive impairment between normal function and dementia,” and look at people already enrolled in a long-term study that prospectively tracks their cognitive health as they age, the Mayo Clinic Study of Aging (MCSA).

The average age of the participants was 79, with the median duration between follow-up examinations being around five years. Of the 1,731 people tracked, 536 people had MCI by the first follow-up visit; but there appeared to be no significant higher risk among those given anesthesia after 40 compared to those never given it. Even in the one subgroup where an association was found, there are other possible explanations beside anesthesia exposure. For instance, it might be the case that people who need vascular surgery are already at risk of MCI and dementia because they have severe atherosclerosis, a known risk factor for both.

Still, as the researchers note, “these results do not exclude the possibility that exposures to anesthesia and surgery or procedures at a more advanced age may be associated with incident MCI.” Similarly, they don’t definitively negate prior research on the very young, which has found some support for a link between anesthesia exposure and later cognitive problems.

"That by no means is established yet. Right now it's just associations, and we and many other people are doing a lot of work to try to see if this really is a problem in children or not," Warner said of this research. "Because of the associations that we've seen, there is more concern in the young than the old, and it will require quite a bit more research to find out what is happening with the children, and if there is a problem, how we can best address it. But for the moment, there is little clinical evidence that anesthesia itself leads to cognitive decline in the elderly — although more research is needed."

Source: Sprung J, Roberts R, Knopman D, et al. Association of Mild Cognitive Impairment With Exposure to General Anesthesia for Surgical and Nonsurgical Procedures. Mayo Clinic Proceedings. 2016.