The Impact of Poor Health on IQ

January 8, 2020 Maria Perrin

On a chilly, cloudy and windy June 1st in Edinburgh, 1932, almost every 11-year-old child in Scotland was given an IQ test. In all, 87,498 tests were administered, and the over the intervening decades the data has been used to study connections between intelligence and aging, disease, and mortality.

 Lothian Birth Cohort Study

The study of the connection between health and IQ is known as cognitive epidemiology. One of the most striking experiments performed in the field is known as the Lothian Birth Cohort Study, co-founded by Scottish psychologist Ian Deary. In September 1999, Dr. Deary began evaluating the subjects of the decades-old intelligence tests (which were originally used, along with results from similar tests conducted in 1947, to determine if large families cause lowered intelligence—they do not).

What he found was remarkable: those with an IQ 15 points higher than average (IQ=115) were 21% more likely to be alive at age 76 than a person with an average IQ of 100.

Correlation Does not Imply Causation

The “chicken and egg problem.” The question is: does higher intelligence cause people to live longer? Or are people who are predisposed to live longer also predisposed to have higher IQs?

In the first case, it’s possible that those with lower IQs are less educated in healthy habits and therefore are more likely to engage in unhealthy lifestyle choices, such as drug abuse, smoking, drunk driving. Conversely those with higher IQs are more likely to exercise, eat healthily etc. There is evidence for this in the Scottish data—in the 1940s, before the health risks were known, those with higher IQs were as likely to be smokers as the general population. However, once the dangers were widely accepted, those with higher IQs were more likely to stop smoking.

In the second case, it’s possible that the same genetic factors are involved in both IQ variation and healthy/unhealthy lifestyle choices.

Similar “chicken/egg” difficulties have been seen in other studies. For example, those who were breastfed as children are more likely to have higher IQs, possibly as a result of omega-3 fatty acids improving brain structure. However, it could be that mothers who breast-feed are more likely to have higher IQs which they pass on to their children.

The Good News

While the participants in the Lothian Study stayed generally in the same IQ percentile over the course of their lives, Dr. Deary estimates that about 25% of intelligence is genetically predetermined. Those who engaged in healthier behaviors over their lives were more likely to improve their IQ scores as they aged.

This link between health and IQ is yet another compelling reason to engage and educate our communities on the importance of achieving and maintaining a healthy lifestyle.


Post note

In September 2019 almost 300 members of the longest-running study on aging celebrated the 20th anniversary of Dr. Deary’s investigation into their intelligence. By that time the data had produced a staggering 512 peer-reviewed scientific articles.

About the Author

Maria Perrin

Maria Perrin is Chief Growth Officer for HMS, where she is responsible for the company’s corporate strategy, marketing, government relations, business development, and oversight of the company’s more than 500 contracts with government and commercial healthcare organizations. She has transformed HMS’ brand and furthered its industry impact through numerous thought leadership and innovation initiatives. Maria rejoined HMS in 2019, after co-founding a successful consulting practice that launched dozens of health tech startups and tech companies in emerging sectors. During her first tenure at HMS, as Chief Marketing Officer and EVP over government and commercial markets from 2008 – 2013, HMS revenue grew fivefold and the company successfully entered the federal market, doubled the volume of state contracts, and expanded services to commercial payers. Prior to HMS, Maria was Senior Vice President, Sales, Marketing, and Business Development for Performant Financial Corp. where she led Performant’s entry into the healthcare market and other sectors. Maria has held financial and operational leadership roles for BestFoods, Nissan and other Fortune 100 companies. She has a BA in Economics from UCLA and an MBA from the University of Miami.

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