The dumbest epidemiology

Last week, the BBC publicised the results of a study which claimed that sugar consumption in early life increases the risk of dementia. People who don’t eat much sugar in the first years of life are supposedly 23 per cent less likely to develop the condition when they are older. “Our findings suggest that limiting sugar during the earliest stages of life may have lasting benefits for brain health,” said the study’s lead author Jiazhen Zheng.

How does he know this? He looked at data from the UK Biobank and found that people born between 1940 and 1953, when sugar was rationed, were less likely to develop dementia than those born afterwards. 

 

Of 15,025 who experienced sugar rationing before birth and during their first year of life, 388 developed dementia. Of 15,256 who experienced sugar rationing before birth and during their first two years of life, 456 developed dementia. Of 23,774 born after sugar rationing, 504 developed dementia. 

 

If you get your calculator out, you will find that these figures show that the rate of dementia actually fell over time, with 2.1 per cent of the youngest cohort suffering from the disease, compared to 2.6 per cent of the oldest cohort and 2.5 per cent of the second group. The claim that the people who endured sugar rationing were 23 per cent less likely to get dementia is based on numbers that have undergone substantial adjustment. 

But that is not the real problem with this study. The real problem is something that has doubtless already occurred to you and that would be obvious even to a small child. If people born between 1940 and 1953 are healthier than people born after 1953, there could be any number of explanations for it. There is no more reason to attribute it to sugar rationing than to anything else, including meat rationing and egg rationing. There is no reason to assume that it has anything to do with diet, nor indeed to anything people do in their first two years of life. These individuals grew up and lived in different times when the prevalence of some diseases declined and others increased. Focusing on one event and giving it the credit for everything that happened afterwards is so stupid that there is a name for it: the post hoc ergo proctor hoc fallacy. 

 

It gets worse. Read about it at The Critic. 

 

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