Urban environments can adversely affect adult's mental health: Study

According to projections, around 2050, nearly two-thirds of the world's population is expected to reside in urban areas, where densely packed structures, increased stress levels, limited access to green spaces, and heightened exposure to substance use are defining features of urban life.

A recent study published in Nature Medicine delved into the impact of the urban environment on the mental well-being of adults, the News Medical site reported.

The study analysed data from the United Kingdom Biobank (UKB), specifically targeting adults aged 41 to 77 years living in urban areas.

Researchers examined information from 156,075 participants, with a subset of over 42,000 individuals undergoing brain neuroimaging (NI).

They assessed 128 urban environment factors across 53 categories and studied their relationship with 21 psychiatric symptoms.

3 Distinct sets of symptoms

The analysis revealed three distinct sets of symptoms associated with specific urban profiles.

The first set, known as the affective symptom group, included feelings of tiredness, lack of enthusiasm, depressive mood, fed-up sentiment, and loneliness.

These symptoms were positively linked to factors like sound and air pollution, urban infrastructure density and traffic, street accessibility, and socio-economic deprivation indices.

Conversely, the presence of nearby green spaces and distance to urban facilities showed negative correlations.

The second set, referred to as the anxiety symptom group, comprised symptoms such as anxious feelings, tension, excessive worrying, nervousness, psychiatric visits, and general nervousness.

This group showed a significant association with a different urban profile, characterised by higher densities of mixed urban infrastructure and leisure places, proximity to the coast, diverse terrain, and variations in vegetation index (NDVI).

On the other hand, anxiety symptoms were negatively correlated with water proximity, distance to energy and waste facilities, and average NDVI.

The third set, categorised as the emotional instability symptom group, encompassed mood swings, feeling miserable or highly strung, neuroticism, sensitivity, irritability, risk-taking, stress, grief, and hurt feelings.

These symptoms demonstrated negative associations with factors like distance to food stores, densities of water and unused land, amenities, and open space.

However, the emotional instability group showed positive correlations with terrain variations and densities of educational facilities, accommodation, and medical or emergency facilities.

Genetic associations

The study also explored genetic associations with the symptom sets.

The affective symptom group showed more than 3,400 significant associations with single-nucleotide polymorphisms (SNPs) in various genes. SNPs refer to the most common type of genetic variation that occurs in individuals.

The strongest associations were found in a supergene candidate located on chromosome 17q21.3 and the corticotropin-releasing hormone receptor 1 (CRHR1) gene.

Similarly, the anxiety symptom group exhibited significant associations with 29 SNPs across nine different genes.

Among these SNPs, rs77641763 stood out as the lead SNP, located in one of the introns of the exonuclease 3'-5' domain containing 3 (EXD3) gene.

Furthermore, the emotional instability symptom group displayed significant associations with 10 SNPs, with the lead SNP being rs77786116.

This SNP was found in the intraflagellar transport 74 (IFT74) gene.

The intraflagellar transport 74 (IFT74) gene is a specific gene that encodes a protein involved in a cellular process called intraflagellar transport (IFT).

Intraflagellar transport is essential for the assembly and maintenance of cilia, which are microscopic, hair-like structures found on the surface of many cells in our body.

Defects or variations in the IFT74 gene can potentially impact the proper functioning of cilia, leading to various health conditions and disorders.

Brain volumes

In addition, brain volumes were examined in relation to the symptom groups and urban profiles.

Certain regional brain volumes were found to be associated with each symptom group and their corresponding urban profile.

A moderated mediation analysis investigated whether genetic differences influenced the associations mediated by brain volumes.

The analysis revealed that gene scores for CRHR1, EXD3, and IFT74 moderated the mediation pathways for the affective, anxiety, and emotional instability groups, respectively.

In this context, gene scores refer to the genetic variations or expression levels of specific genes. These gene scores were found to have an impact on how the associations between the urban environment, brain volumes, and mental health symptoms were mediated.

Moderating the mediation pathway means that these gene scores influenced or altered the relationship between the urban environment and the specific symptom groups (affective, anxiety, and emotional instability).

In other words, the gene scores of CRHR1, EXD3, and IFT74 played a role in shaping the effects of the urban environment on mental health symptoms, ultimately influencing the observed associations.

Overall, the study concluded that specific urban environmental profiles were correlated with distinct symptom groups.

The first urban profile, linked to affective symptoms, represented a densely populated, disadvantaged inner-city neighbourhood characterised by air pollution, deprivation, traffic, limited green space, and close proximity to urban facilities.

In contrast, the second urban profile inversely correlated with anxiety symptoms and reflected areas with ample green spaces, lakes, rivers, seas, and significant distances from energy and waste facilities.

The third urban profile, associated with emotional instability symptoms, showed a lower variance but was positively correlated with urban infrastructure and land use density.

These findings emphasise the potential influence of different urban environments on specific mental health symptoms, providing valuable insights into the complex relationship between urban living and well-being.