"There is no longer any doubt that what happens in the brain influences what happens in the body. When facing a health crisis, actively cultivating positive emotions can boost the immune system and counter depression. Studies have shown an indisputable link between having a positive outlook and health benefits like lower blood pressure, less heart disease, better weight control and healthier blood sugar levels."Actively cultivating positive emotions may "boost the immune system" in the lab in some artificial setting based on some surrogate measure, but it does not give us information about what we want to know: does it make us healthier and more resistant to disease? The rest of that selection involves the highly fraught associations problem described above. Chicken, egg, or neither?
Also trending right now is Gretchen Reynold's article "Why Deep Breathing May Keep Us Calm":
"The scientists confirmed that idea in a remarkable study published last year in Nature, in which they bred mice with a single type of pacemaker cell that could be disabled. When they injected the animals with a virus that killed only those cells, the mice stopped sighing, the researchers discovered. Mice, like people, normally sigh every few minutes, even if we and they are unaware of doing so. Without instructions from these cells, the sighing stopped."
"In the two earlier studies, there was a negative association; maternal age 35-39 at birth was associated with poorer cognitive scores in the children, tested a decade later; the children who had been born to mothers 25-29 did better. On the other hand, for the most recent study, that association was reversed; the children born to the 35- to 39-year-olds did significantly better on the cognitive testing than the children born to the younger mothers."In addition to the problem of association, we are told that in different epochs children of different age mothers do either "poorer" or "better". When I read that article, I immediately suspected that the statistically significant differences (had they not been they would not have been published, right?) referred to were likely to be very small. The standard deviation (SD) for IQ scores is 15 points - thus a 3 point difference represents one fifth of a SD of IQ. My guess was that any differences that were found were on the order of 3 points. Perhaps not negligible, but nothing to write home about and probably not cause for any celebration even if there were something you could do about it. The abstract of the index report is here and it says:
"Results For the 1958-1970 cohorts, maternal ages 35-39 were associated with 0.06 (95% CI: -0.13, 0.00) and 0.12 (95% CI: -0.20, -0.03) standard deviations (SD) lower cognitive ability compared to mothers in the reference category (25-29), while for the 2001 cohort with 0.16 (95% CI: 0.09-0.23) SD higher cognitive ability."As I suspected, the differences are small (on the order of one tenth to one fifth of a SD). The effect is small enough that I'm not sure there was a "problem" for the 1958-1970 cohort, who in delaying maternity sacrificed 1-2 IQ points in their children, or that there is suddenly "good news for older mothers" since the older cohort has gained a couple of IQ points, assuming the research result is true.
In this excellent JAMA article raining criticism on surrogate endpoints, Lipska and Krumholz, two accomplished and respected researchers, fail to report the strength of the evidence they tout:
"For example, treatment with empagliflozin (a sodium-glucose cotransporter 2 inhibitor) and treatment with liraglutide (a glucagon-like peptide 1 [GLP-1] agonist) both significantly reduced the risk of major cardiovascular events, mortality from cardiovascular causes, and mortality from any cause when compared with placebo.4,5"Reference 4 is the FDA-mandated safety trial by Marso. Table 1 shows that the difference in the primary outcome (death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke) was 3.4 such events per 100 persons per year for liraglutide versus 3.9 for placebo, a difference of .5 events per 100 persons per year or one half of one percentage point. For those who prefer the number needed to treat (NNT) that's 200 persons that need to be treated per year to prevent one event with liraglutide. A rate of 0.5% would not sway me to take liraglutide versus another drug were I choosing a treatment for diabetes, unless cost, side effects, and convenience were also all aligned in its favor. I have called this problem the "therapeutic paradox" not realizing that Geoffrey Rose dubbed it the "prevention paradox" 30 years before I. These paradoxes result because minuscule effects on the individual level are not enough to sway decisions, but on the population level, thousands of events are prevented if a particular course is preferred, because of scaling. An elaboration of this concept is beyond our scope here and interested readers are referred to the links above. The point is that there can be a true positive research result that is of such a small magnitude that it is negligible or useless to guide decision making on the individual level - other factors will have much greater weight, whether it involves the decision of when to have a child, or what drug to take to control your diabetes.
In these three ways (and perhaps others) even true research findings are not adequate to guide decisions and are often best ignored. Even if we assume that a finding is true, a course which Ioannidis and others have strenuously warned us against, most research findings are useless for the individual faced with a decision because they report associations rather than causal pathways, they report surrogate outcomes or surrogate experimental models, or they report "positive" findings that are simply too small in magnitude to matter for individual decisions.