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A cohort study looked at over five million adults and over 850,000 children between the ages of five and eleven who received care at Kaiser Permanente Northern California during the ten-year period from the beginning of 2007 through the end of 2016. At any given time, KPNC serves roughly four million persons. It is representative of the population of the region, except for the highest and lowest income strata.

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‍ADHD Diagnosis Rates:

• Adults: Diagnosis rates rose from 0.43% in 2007 to 0.96% in 2016.
• Children: Diagnosis rates went up from 2.96% to 3.74%, nearly four times higher than in adults.

Diagnosis Rates by Ethnicity:

• Non-Hispanic whites had the highest adult diagnosis rates, increasing from 0.67% to 1.42%.
• American Indian/Alaska Native (AIAN): Rates grew from 0.56% to 1.14%.
• Black and Hispanic adults had similar rates: Black adults increased from 0.22% to 0.69%, and Hispanic adults rose from 0.25% to 0.65%.
• Asian adults had the lowest rates (0.11% to 0.35%), followed by Native Hawaiian/Pacific Islanders (0.11% to 0.39%).

ADHD Diagnosis and Age:

The likelihood of being diagnosed with ADHD dropped sharply with age.

(When compared to 18-24-year-olds):

• 25-34-year-olds were 16% less likely.
• 35-44-year-olds were 33% less likely.
• 45-54-year-olds were less than half as likely.
• 55-64-year-olds were less than a quarter as likely.
• Adults over 65 were about 5% as likely.

This matches findings from other studies showing that ADHD diagnoses become less common with age.

‍Other Factors:

• Adults with higher education levels were twice as likely to be diagnosed as those with less education.
• Household income had little effect on diagnosis rates.
• Women were slightly less likely to be diagnosed than men.

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ADHD and Comorbidity:

Adults with ADHD were more likely to have other mental health conditions:

• Eating disorders: 5 times more likely.
• Bipolar disorder or depression: Over 4 times more likely.
• Anxiety: More than twice as likely.
• Substance abuse: Slightly more likely.

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Key Findings:

1. Rising ADHD Diagnosis Rates: The increase in diagnoses may be due to better recognition of ADHD by doctors and greater public awareness during the study period.
2. Differences by Ethnicity: The differences in diagnosis rates by ethnicity could be related to access to healthcare, cultural attitudes toward mental health, or even attempts to obtain ADHD medications for non-medical reasons, which may be more common among white patients.

Conclusion:

The authors speculate that rising rates of diagnosis “could reflect increasing recognition of ADHD in adults by physicians and other clinicians as well as growing public awareness of ADHD during the decade under study.” Turning to the notable differences by ethnicity, they note, “Racial/ethnic differences could also reflect differential rates of treatment-seeking or access to care. … Racial/ethnic background is known to play an important role in opinions on mental health services, health care utilization, and physician preferences. In addition, rates of diagnosis- seeking to obtain stimulant medication for non-medical use may be more common among white vs nonwhite patients.” They conclude, “greater consideration must be placed on cultural influences on health care seeking and delivery, along with an increased understanding of the various social, psychological, and biological differences among races/ethnicities as well as culturally sensitive approaches to identify and treat ADHD in the total population.”

The study highlights that many cases of adult ADHD go undiagnosed. Research shows about 3% of adults worldwide have ADHD, but this study found that less than 1% are diagnosed by doctors. This points to the need for better training for clinicians to recognize, diagnose, and treat ADHD in adults. It also emphasizes the importance of understanding cultural factors that affect how people seek and receive care.

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