Danish health care is universal and free. That means there is very complete data available that covers the entire population. The health registers are linked to other national registers that provide access to socioeconomic information. That offers unusual opportunities to research correlations across an entire national population.
Moreover, the health care system requires a high standard for diagnosis of ADHD - evaluation by specialist doctors or psychiatrists rather than a general practitioner. An exception is when parents seek a diagnosis from a private practicing child psychiatrist, in which case diagnostic registration is not mandatory and data is therefore incomplete.
A trio of Danish researchers used the country' national registers to conduct a nationwide population cohort study to explore the cumulative effects of social disadvantages as risk factors for being diagnosed with ADHD.
They looked at all 632,725 children born in Denmark during the 1990s, of which 23,287 (3.7 percent) either had a registered diagnosis in the Patient Registry or else were undergoing ADHD treatment before age 18. Of these, 12,610 children had a registered ADHD diagnosis and entered medical treatment, 4,049 children had a registered diagnosis with no medical treatment, and 6,628 children entered medical treatment with no registered diagnosis. The latter were presumably diagnosed by private practicing psychiatrists. Adjustments were made for gender, immigrant status, birth characteristics (weight, gestational age), single-parenthood, parent ADHD diagnosis, and the number of children in the household.
The study determined that parental educational attainment had the largest effect on the risk of ADHD. Having parents who completed no more than the minimum compulsory education was associated with a 3.5 percentage point higher risk of getting an ADHD diagnosis. Completing no more than upper secondary education was associated with a 1.3 percent higher risk. But there was a sharp bifurcation in the two alternative components of upper secondary education. Children of parents who completed a vocational track faced a 1.7 percent increase in risk, whereas those whose parents completed a college preparatory track faced a negligible 0.17 percent increase.
Parental unemployment also had a significant effect. Youths whose parents were unemployed most of the year faced a 2.1 percent higher risk of ADHD, whereas those whose parents were unemployed less than half the year faced a 1.3 percent higher risk.
Relative income poverty had a comparable impact. Children of parents in the lowest income quintile faced a 2.3 percent higher risk of ADHD than those of parents in the uppermost income quintile. Those in the second-lowest quintile faced a 1.9 percent higher risk than those in the uppermost quintile; those in the middle quintile a 1.3 percent higher risk, and those in the second-highest quintile a 0.8 percent higher risk.
All three cases showed a dose-response relationship, in which higher gradations of social disadvantage were associated with higher levels of risk.
Since these social disadvantages often overlap, the researchers looked at combinations as well and found them to be roughly additive in effect. Parental unemployment plus relative income poverty was associated with a 1.9 percent higher risk of offspring ADHD. Parental unemployment plus completion of no more than compulsory education was associated with a 3.2 percent higher risk. Parental relative income poverty plus completion of no more than compulsory education produced a 4.2 percent higher risk. Finally, Parental relative income poverty plus completion of no more than compulsory education plus unemployment was associated with a 4.9 percent higher risk.
The authors concluded, "This study shows that specific and well-measured parental social disadvantages in terms of unemployment, relative income poverty, and low educational attainment independently affect the risk of ADHD."
Maria Kellow, Chunsen Wu, Carsten Obel, "Cumulative social disadvantage and risk of attention deficit hyperactivity disorder: Results from a nationwide cohort study," SSM - Population Health (2020) 10, 100548, https://doi.org/10.1016/j.ssmph.2020.100548.
_logo%201.svg)
