The study shows a clear link between each of these things and risk of a future diagnosis of Parkinson's... this is interesting because it might mean that controlling blood pressure and diabetes etc in mid-life might lower risk of Parkinson's in the future.
The big advantages are the size of the study (more than 17 million people), which in turn is a large proportion of the entire population over the age of 40 in South Korea. Another big advantage is that there were relatively few exclusions from the study where data were missing for participants. Both of these facts guard against incorrect results.
However the disadvantages of the study centre on the fact that it does not adequately take account of reverse causation, that is, undiagnosed Parkinson's causing changes in blood pressure, and the risk of high cholesterol, diabetes and obesity. You have to remember that Parkinson's is 'clinical diagnosis' which means that it is made by an expert on the basis of the clinical examination findings. The doctors assessing these patients in routine healthcare settings were not looking for signs of Parkinson's specifically and therefore subtle signs could have easily been missed.
Parkinson's changes in the brain are likely to be happening 5, 10, 15 or more years before that diagnosis is eventually made. This means that event though the authors of this study excluded new case of Parkinson's within 4 years of finding of high blood pressure, high cholesterol, diabetes and obesity, that is probably not a sufficient amount of time. Increasingly sedentary lifestyle in the early and undiagnosed phase of Parkinson's could have resulted in an increased likelihood of some of these factors.
It is also likely that people with increasing features of the 'metabolic syndrome' are at higher risk of death before they get diagnosed with Parkinson's, which in itself could have resulted in biased results. However, the authors took account of this in one of their analyses and even mentioned that they did this following a comment from someone who reviewed their paper. As a footnote, I have never seen this mentioned in a paper before (that a reviewer asked for something and the authors included it) even though it frequently happens. I think it is great! The peer review process for scientific papers often improves them (sometimes it doesn't !) and we should feel able to acknowledge improvements at every stage before publication...
- Alastair Noyce
Ga Eun Nam, Seon Mee Kim , Kyungdo Han, Nan Hee Kim, Hye Soo Chung, Jin Wook Kim, Byoungduck Han, Sung Jung Cho, Ji Hee Yu, Yong Gyu Park, Kyung Mook Choi
PLOS Medicine
Published: August 21, 2018
Background
The association of metabolic syndrome (MetS) with the development of Parkinson disease (PD) is currently unclear. We sought to determine whether MetS and its components are associated with the risk of incident PD using large-scale cohort data for the whole South Korean population.
Methods and findings
Health checkup data of 17,163,560 individuals aged ≥40 years provided by the National Health Insurance Service (NHIS) of South Korea between January 1, 2009, and December 31, 2012, were included, and participants were followed up until December 31, 2015. The mean follow-up duration was 5.3 years. The hazard ratio (HR) and 95% confidence interval (CI) of PD were estimated using a Cox proportional hazards model adjusted for potential confounders. We identified 44,205 incident PD cases during follow-up. Individuals with MetS (n = 5,848,508) showed an increased risk of PD development compared with individuals without MetS (n = 11,315,052), even after adjusting for potential confounders including age, sex, smoking, alcohol consumption, physical activity, income, body mass index, estimated glomerular filtration rate, and history of stroke (model 3; HR, 95% CI: 1.24, 1.21–1.27). Each MetS component was positively associated with PD risk (HR, 95% CI: 1.13, 1.10–1.16 for abdominal obesity; 1.13, 1.10–1.15 for hypertriglyceridemia; 1.23, 1.20–1.25 for low high-density lipoprotein cholesterol; 1.05, 1.03–1.08 for high blood pressure; 1.21, 1.18–1.23 for hyperglycemia). PD incidence positively correlated with the number of MetS components (log-rank p < 0.001), and we observed a gradual increase in the HR for incident PD with increasing number of components (p < 0.001). A significant interaction between age and MetS on the risk of incident PD was observed (p for interaction < 0.001), and people aged ≥65 years old with MetS showed the highest HR of incident PD of all subgroups compared to those <65 years old without MetS (reference subgroup). Limitations of this study include the possibilities of misdiagnosis of PD and reverse causality.
Conclusions
Our population-based large-scale cohort study suggests that MetS and its components may be risk factors of PD development.
Kaplan–Meier curves of incidence probability of Parkinson disease (PD) for up to 7 years according to the number of metabolic syndrome (MetS) components.
Having an increased number of MetS components was associated with increased risk of PD development during the follow-up period compared to having no components (log-rank p < 0.001).
All this could just mean that the gut bacteriome rules our destiny even more than we can imagine. Different gut bacterial, fungal, prion, virus (and who knows what else) populations and balances and various diets make any such conclusions open to doubt, not in their veracity, but in their certainty.
ReplyDeleteOne might even suspect that humans and other animals are all part of a giant multi-century in vivo trial of gut occupants in varying proportions. This will conclude when the combination ideal to the inhabitants of the gut is found. We are only laboratory rats.