Research & Publications Drawn from CHDS Data

More adults under the age of 50 are being diagnosed with cancer, and scientists still aren't sure why. This study asked whether things that happen during pregnancy and very early in life might play a role. The researchers used the CHDS data. By age 40, 41 of the Study Members had developed cancer. Because CHDS tracks 158 different things about each person but only has a small number of cancer cases, the usual ways of analysing the data can miss important patterns. So the team used a computer-based method called machine learning to spot connections that simpler methods cannot. Four things stood out. Pregnancies where the mother received antenatal care at a hospital or clinic, took vitamins, or took cough medicine were each linked to a higher chance of the child developing cancer before age 40. The authors think these patterns are clues, not causes. For example, mothers who get hospital-based care often have more complicated pregnancies, and mothers who take cough medicine usually have an infection. It is likely the underlying conditions are the contributing factors or events, and not the care setting or the medicines themselves. 

Researchers used data from the CHDS, which has followed 1,265 people born in Christchurch in 1977 from birth into their forties. They looked at whether young people who showed many signs of ADHD (such as inattention, hyperactivity, and impulsiveness) between ages 14 and 16 went on to face more difficulties as adults. The 25% of teenagers with the most ADHD symptoms were more likely to develop problems with alcohol, tobacco, cannabis and other drugs; experience depression, anxiety and suicidal thoughts; be arrested or commit offences; have unstable relationships; and earn less, own a home less often, and live in tougher financial conditions. Once the researchers accounted for things like family hardship, abuse in childhood, and overlapping conditions such as conduct disorder, many of these links became weaker — but the connections to substance use and criminal offending stayed clear. Almost none of this group received ADHD medication, so the findings reflect what happens when ADHD symptoms go largely untreated. The authors call for better long-term support, earlier identification, and improved access to treatment, particularly for adults who may have undiagnosed ADHD.

Air pollution is well known to harm physical health, particularly the heart and lungs, but its connection to mental health and behaviour is less clear. This study used data from the CHDS across four decades, to ask whether long-term exposure to common air pollutants is linked to depression, anxiety, suicidal thoughts, or problems with alcohol, tobacco, cannabis and other drugs in adulthood. The researchers matched each person's home addresses across their life to estimates of air pollution levels in their neighbourhoods, including fine and coarse particle pollution (PM₂.₅ and PM₁₀) and nitrogen dioxide (NO₂) from traffic and industry. At first, several connections appeared: people exposed to higher pollution levels seemed slightly more likely to experience mental health and substance use problems. However, once the researchers accounted for other influences almost all of these connections faded, including family background, education, income, where people lived, and access to greenspace. The only link that remained was a small association between fine particle pollution (PM₂.₅) and nicotine dependence. The authors suggest that, in this New Zealand setting, factors closer to home — such as family circumstances, social conditions, and individual life experiences — appear to matter more for adult mental health than air pollution exposure, although they emphasise that further research using more complete pollution data is needed before firm conclusions can be drawn. The CHDS made this analysis possible by providing decades of detailed residential and health information that few other studies anywhere in the world can match.

Amphetamines (including methamphetamine, sometimes known as speed or ice) are known to be linked with mental health problems, but until now it has been unclear which comes first: does drug use lead to poor mental health, or do mental health struggles lead to drug use? To explore this, researchers combined information from four long-running studies of young people in Australia and New Zealand, including the Christchurch Health and Development Study (CHDS), which contributed data from 1,056 of its participants. Together, these cohorts followed 7,527 people from adolescence (ages 10–17) through young adulthood (ages 18–30). The researchers found that the relationship runs in both directions. Young people who used amphetamines at least monthly during adolescence were about 21% more likely to experience mental health difficulties as young adults. At the same time, those who experienced mental health difficulties as adolescents were about 19% more likely to use amphetamines regularly in young adulthood. Interesting differences appeared between males and females. For young men, the stronger pathway was from drug use to later mental health problems. For young women, the stronger pathway ran the other way (from mental health difficulties to later amphetamine use) possibly reflecting patterns of self-medication. Although the authors are careful to note that these associations cannot definitively prove cause and effect, the findings suggest that addressing one of these problems early may help prevent the other. The CHDS's long-term data on substance use, mental health, and a wide range of family and individual factors made it a vital contributor to this Australasian collaboration, allowing researchers to study a relatively uncommon behaviour (amphetamine use) with greater statistical strength than any single cohort could achieve alone.