Israel has a military draft that applies to males and females alike, except orthodox women and orthodox male seminary(yeshiva) students, who are exempt. Upon turning 17 every Israeli undergoes a medical review, including both a physical and psychiatric assessment, in preparation for the draft. The Draft Board Registry maintains comprehensive health information on all unselected Israelis until they turn 21. The registry also tracks all family members of draft registrants, including full siblings.
An Israeli study team used registry records from 1998 through2014 to obtain data for a total of over a million individuals (1,085,388). Because of the exemption for orthodox women, 59% were male.
The team identified 903,690 full siblings in the study population (58% males), including 166,359 male-male sibling pairs, 104,494 female-female sibling pairs, and 197,571 opposite-sex sibling pairs.
Next, the team identified all cases in the study population with a diagnosis of a psychiatric disorder, low IQ (≥2 standard deviations below the population mean), Type-1 diabetes, hernia, or hematological malignancies. It matched each case with ten age- and sex-matched controls selected at random from the study population. Then, for each case and case-matched controls, it identified all siblings.
There were 3,272 cases receiving treatment for ADHD, 2,128 with autistic spectrum disorder, 9,572 with severe/profound intellectual disability, 7,902 with psychotic disorders, 9,704 with mood disorders, 10,606with anxiety disorders, 24,815 with personality disorders, 791 with substance abuse disorders, 31,186 with low IQ, 2,770 with Type-1 diabetes, 30,199 with a hernia, and 931 with hematological malignancies.
Draftees with ADHD were five and a half times more likely to have a sibling with ADHD than controls.
There were no significant associations between ADHD and any of the somatic disorders - Type-1 diabetes, hernia, or hematological malignancies - nor between ADHD and low IQ.
There were also no significant associations between ADHD and autism spectrum disorder, severe/profound intellectual disability, mood disorders, and substance use disorders.
On the other hand, draftees with ADHD were more than 40% more likely to have siblings with anxiety or personality disorders than controls.
Surprisingly, draftees with ADHD were less than half as likely to have siblings with psychotic disorders than controls.
There were some limitations. The psychiatric classification system used by the Israeli military did not permit assessing the risk of bipolar disorder and depression separately. That meant having to use a broader category of mood disorders, including both disorders. In addition, the military diagnostic system does not allow diagnosis of comorbid psychiatric disorders in the same individual, instead of assigning only the most severe diagnosis.
Persons with type 1 diabetes were found to be eight times more likely to be diagnosed with ADHD than those who were not diabetic.
Taiwan has a mandatory single-payer universal health insurance system, the National Health Insurance (NHI), that records diagnoses and prescriptions across virtually the entire resident population. Out of the roughly 28 million residents covered by NHI, a randomly assigned sample of 3 million is tracked in the Taiwan National Health Insurance Research Database(NHIRD).
Expert panels have to confirm all diagnoses of severe systemic autoimmune diseases, ensuring a high level of accuracy.
A Taiwanese study team availed itself of these records to explore the link between type 1 diabetes mellitus (T1DM) and ADHD. ADHD diagnoses were made by board-certified psychiatrists, based on comprehensive interviews and clinical judgment.
The team found a total of 6,226 cases diagnosed with T1DM in the decade from 2001 through 2010 and followed them through the end of 2001. It matched each case with ten age- and sex-matched non-T1DM controls from the same database, for a total of 62,260 controls.
Persons with type 1 diabetes were found to be eight times more likely to be diagnosed with ADHD than those who were not diabetic. There was no difference in the risk ratio between youth and adults. The risk of ADHD among females with T1DM was only slightly lower than among males: sevenfold greater, rather than 8.5 times greater.
The authors concluded, "Our findings indicate the importance of the close monitoring of the mental health condition of patients with T1DM by clinicians ... The exact path of mechanisms between T1DM and major psychiatric disorders should be elucidated in future studies."
Statistically significant exposure-response trend found linking miscarriage and ADHD
Spontaneous abortion is the medical term used for what is more commonly known as miscarriage. It means the unintended loss of an embryo or fetus before the 20th week of pregnancy. This must not be confused in any way with induced abortion, which is a deliberate and intentional act to terminate a pregnancy.
Most miscarriages occur when the fetus is not developing properly. Among the major causes of miscarriage are chromosomal abnormalities, birth defects, abnormal hormonal imbalances, infections, and exposure to toxins.
A team of Chinese researchers used the Danish national registers to explore a nationwide cohort for associations between previous miscarriage and ADHD in subsequent offspring. They included all 1.1 million births in Denmark over the 17 years from 1995 through 2012. They excluded all children with chromosomal abnormalities, those born either extremely early (after less than 22 weeks gestation) or extremely late (greater than 45 weeks), and those for whom this information was missing. That left over one million children in the study cohort.
The team classified children as having ADHD either based on a recorded hospital diagnosis or after receiving ADHD medication prescriptions at least twice after the age of 3 years. A total of 25,747 children were identified as ADHD individuals (554 mothers having at least two miscarriages, 3,087 mothers having one miscarriage, and 22,106 mothers without miscarriage). The average age of the first ADHD diagnosis was 10 years.
Just over 130,000 children (12.2%) were born to mothers who had at least one miscarriage. Of these, just under 113,000 (10.6%) were born to mothers with a single miscarriage before birth, and just over 17,000 to mothers with more than one prior miscarriage.
Based on previous research, the team identified potential confounders, including sex, preterm birth (less than 37 weeks), low birth weight, small for gestational age, low Agar score (performed right after birth to assess the risk of infant mortality), maternal and paternal ages at birth, maternal diabetes, maternal hypothyroidism, maternal smoking during pregnancy, maternal education level, maternal and paternal psychiatric disorders before birth.
After adjusting for these possible confounders, children of mothers with a single prior miscarriage were 9% more likely to develop ADHD than those of mothers without any miscarriage. Children of mothers with two or more prior miscarriages were 22% more likely to be diagnosed with ADHD. This upward exposure-response trend was statistically significant.
Preterm birth was found to be the strongest confounding mediator of this trend but accounted for under 4% of the association. The authors concluded, "the observed associations were independent of several factors, such as maternal socioeconomic status, type of spontaneous abortion, parental history of psychiatric disorders, pregnancy characteristics (maternal smoking status, infection, diabetes and hypothyroidism status during pregnancy)and birth outcomes (low birth weight, preterm birth, low Agar score, and small for gestational age)."
They also noted that given the frequency of miscarriages, affecting more than one in eight women, "a small increase of neurodevelopmental problems in offspring could have major public health implications."
All Swedish residents have their health records tracked through unique personal identity numbers. That makes it possible to identify psychiatric and medical disorders with great accuracy across an entire population, in this case encompassing more than five and a half million adults aged 18 to 64. A subgroup of more than 1.6 million persons between the ages of 50 and 64 enabled a separate examination of disorders in older adults.
Slightly over one percent of the entire population (about 61,000) was diagnosed with ADHD at some point as an adult. Individuals with ADHD were nine times as likely to suffer from depression as were adults not diagnosed with ADHD. They were also more than nine times as likely to suffer from anxiety or a substance use disorder, and twenty times as likely to be diagnosed with bipolar disorder. These findings are very consistent with reports from clinical samples in the USA and Europe.
Adults with ADHD also had elevated levels of metabolic disorders, being almost twice as likely to have high blood pressure, and more than twice as likely to have type 2 diabetes. Persons with ADHD but without psychiatric comorbidities were also almost twice as likely to have high blood pressure, and more than twice as likely to have type2 diabetes.
Similar patterns were found in men and women with ADHD, although comorbid depression, bipolar disorder, and anxiety were moderately more prevalent in females than in males, whereas substance use disorder, type 2 diabetes, and hypertension were more prevalent in males than in females.
ADHD was less than a third as prevalent in the over-50 population as in the general adult population. Nevertheless, individuals in this older group with ADHD were twelve times as likely to suffer from depression, anxiety, or substance use disorders, and more than 23 times as likely to be diagnosed with bipolar disorder as their non-ADHD peers. They were also 63% more likely to have high blood pressure, and 72% more likely to have type 2 diabetes.
The authors noted, "Although the mechanisms underlying these associations are not well understood, we know from both epidemiologic and molecular genetic studies that a shared genetic predisposition might account for the coexistence of two or more psychiatric conditions. In addition, individuals with ADHD may experience increased difficulties as the demands of life increase, which may contribute to the development of depression and anxiety." As for associations with hypertension and type 2 diabetes, these "might reflect health risk behaviors among adult patients with comorbid ADHD in addition to a shared biological substrate. As others have noted, inattention, disinhibition, and disorganization associated with ADHD could make it difficult for patients to adhere to treatment regimens for metabolic disorders." They concluded that "Clinicians should remain vigilant for a wide range of psychiatric and metabolic problems in ADHD affected adults of all ages and both sexes."