This next study (just skip if you're not interested and I leave it here for whomeverJulie G wrote: ...
) isn't any more definitive, or current, than the last one I posted here, and it focused on mortality not dementia. Nevertheless, I found it interesting and nuanced, and I still think it's possible there may be more significance to BMI variation over time than we realize? I'm not at all qualified to weigh in with any opinion on this, so FWIW lol!:Association of body mass index and weight change with all-cause mortality in the elderly (2006, self reporting, n=13,000+)
This is alot of weeds (which are said to be good for the environmentAbstract
The authors explored the relation of body mass index (BMI; weight (kg)/height (m)2) and weight change to all-cause mortality in the elderly, using data from a large, population-based California cohort study, the Leisure World Cohort Study. They estimated relative risks of mortality associated with self-reported BMI at study entry, BMI at age 21 years, and weight change between age 21 and study entry. Participants were categorized as underweight (BMI <18.5), normal weight (BMI 18.5-24.9), overweight (BMI 25-29.9), or obese (BMI ≥30). Of 13,451 participants aged 73 years (on average) at study entry (1981-1985), 11,203 died during 23 years of follow-up (1981-2004). Relative to normal weight, being underweight (relative risk (RR) = 1.51, 95% confidence interval (CI): 1.38, 1.65) or obese (RR = 1.25, 95% CI: 1.13, 1.38) at study entry was associated with increased mortality. People who were either overweight or obese at age 21 also had increased mortality (RR = 1.17, 95% CI: 1.09, 1.25). Participants who lost weight between age 21 and study entry had increased mortality regardless of their BMI category at age 21. Obesity was significantly associated with increased mortality only among persons under age 75 years and among never or past smokers. This study highlights the influence on older-age mortality risk of being overweight or obese in young adulthood and underweight or obese in later life. Copyright © 2006 by the Johns Hopkins Bloomberg School of Public Health All rights reserved.
from Discussion
Both weight loss between age 21 and later life (regardless of weight at age 21) and being underweight at age 21 but not gaining weight later in life were associated with increased mortality. Conversely, being of normal weight at age 21 and gaining weight by late adulthood was associated with decreased all-cause mortality.
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The variations in the shape of the association between BMI and all-cause mortality among studies may be due to differences in the age composition of the cohorts, the length of follow-up, and the variables that were adjusted for in the analyses, as well as inclusion or exclusion of smokers or early deaths. Two studies with long follow-up in the elderly have found a reverse J-shaped association (2, 23). The results of these studies agree with our finding that persons in the lowest weight category, regardless of age, adjustment for other confounders, or exclusion of early deaths, have the highest mortality.
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It may also be a mix, especially in the elderly, of persons with low muscle mass and persons with low fat mass (30). Adjustments for recent weight changes and other measures of assessing body composition are important in order to pinpoint the reasons for increased mortality among the underweight elderly. Nonetheless, our results are fairly robust in showing that underweight elderly have higher mortality than normal-weight elderly.
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While the authors of a recent meta-analysis of the association between adiposity and all-cause mortality emphasized the importance of adjusting for physical activity (5), the summary relative risk for an elevated BMI from the studies that included physical activity as a covariate (RR = 1.23) was almost identical to the risk from the studies that did not (RR = 1.24). Consistent with this finding, our results were similar regardless of whether or not we adjusted for physical activities.
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We were able to adjust for several important confounding variables and to explore the modifying effects of smoking status, age, and gender. Our study highlights the risks on mortality in older age of being overweight or obese in young adulthood and underweight or obese in later life.
) . I do agree that the CDC's and Dr. Bredesen's BMI range overall are good guides, but I wonder if it would be more optimal to include a combination of metrics in some sort of formula that would give more precise feedback about one's … would phenotype be the right word here? It could include any or all of muscle strength, muscle mass, viceral vs. subcutaneous fat …After all that I finally did what I should have done up front with this article, especially given its age. I looked at the "cited by" references and found one from April of this year:
Life-long body mass index trajectories and mortality in two generations
I keep finding more on this notion of the importance of BMI trajectories. So I'll leave it alone with this quite interesting one from 2019, since it focused on dementia:Abstract
Purpose: To identify life-long body mass index (BMI) trajectories across two related generations and estimate their associated mortality risks and population attributable deaths.
Methods: We use prospective cohort data from the Framingham Heart Study (1948-2011) original (4576 individuals, 3913 deaths) and offspring (3753 individuals, 967 deaths) cohorts and latent trajectory models to model BMI trajectories from age 31 to 80 years. Survival models are used to estimate trajectory-specific mortality risk.
Results: We define seven BMI trajectories among original cohort and six among offspring cohort. Among original cohort, people who are normal weight at age 31 years and gradually move to overweight status in middle or later adulthood have the lowest mortality risk even compared to those who maintain normal weight throughout adulthood, followed by overweight stable, lower level of normal weight, overweight downward, class I obese upward, and class II/III upward trajectories. Mortality risks associated with obesity trajectories have declined across cohorts, while the prevalence of high-risk trajectories has increased.
Conclusions: The mortality impact of weight gain depends on an individual's BMI trajectory. Population attributable deaths associated with unhealthy weight trajectories have grown over generations because the prevalence has increased, offsetting the decline in trajectory-specific mortality risks.
Five-decade trajectories in body mass index in relation to dementia death: follow-up of 33,083 male Harvard University alumni
So, without diving into every variable in this "research," if someone experiences significant weight loss without trying to from about age 50, it could be a warning sign. Contrast that with someone who loses weight intentionally while improving cardio and metabolic markers.Background:
In prospective cohort studies, obesity has been linked with a lower risk of subsequent dementia. Reverse causality, whereby neurodegeneration preceding overt dementia symptoms may lower weight, is a possible explanation of these findings. To explore further the weight–dementia association we followed people from early adulthood, an age at which neurodegeneration has typically yet to begin.
Results:
We found no association between early life BMI and subsequent dementia (age-adjusted HR 0.94, 95% CI 0.85, 1.04). We identified two latent class groups based on different BMI trajectories—“early decliners” whose BMI began to decline around age 50 years and “late decliners” whose BMI declined about two decades later. The former experienced a raised risk of dementia-related death compared to the latter (multivariable-adjusted HR 1.57, 95% CI 1.14, 2.17). Expected associations were identified between CVD risk factors and CVD death.
Conclusions:
In a population likely to be free of dementia neuropathology at BMI measurement, we found no association between BMI at baseline and subsequent dementia-related death. Earlier decline in BMI was, however, associated with dementia, which suggests that findings associating BMI with dementia risk may be influenced by reverse causality.
On almost all if not every doctor's office intake form they ask if you've experienced any unexpected weight loss. I wonder, if a patient has, whether if they are in mid-life the doctor considers early neurodegenerative changes as a possible cause. I suspect not at this time. It would seem that they still need to isolate just how early neurodegeration could cause weight loss … assuming this is all replicated and passes a rigorous sniff test.
The verbiage that we settled on in the book to encourage readers to incorporate frame size and muscle composition (with BMI) while remaining vigilant against excessive weight loss can be found below.
