Lausanne: People with a predisposition to obesity
will be more likely to develop the condition if they are faced with
disadvantageous socioeconomic conditions. In Lausanne, the probability
of being overweight is therefore higher in the west than the east of the
city, because levels of deprivation are higher in the west. Nutrition,
lifestyle and the environment interact with an individual’s genes and
are likely to influence their body mass index (BMI). The level of
deprivation is therefore a decisive factor. These
are the conclusions of the study published jointly by the University of
Exeter Medical School, Lausanne University Hospital (CHUV) and the
Ecole polytechnique fédérale de Lausanne (EPFL) in the International Journal of Epidemiology.
The researchers were able to confirm the initial results found by
analysing 120,000 individuals drawn from the UK’s biobank. Around 6,000
inhabitants of the capital of Vaud (the CoLaus study) were used to test
and confirm the findings.
Among the
study’s co-authors are Zoltán Kutalik (Institute of Social and
Preventive Medicine, IUMSP), Idris Guessous (Policlinique médicale
universitaire, PMU), researchers at CHUV and Stéphane Joost, from the
Geographic Information Systems Laboratory (LASIG) at EPFL. They have
been working to identify the causes of obesity for several years. In
2014, an initial study on the geographical distribution of BMI in the city of Geneva
revealed that a difference in income was not enough to explain the
spatial distribution of people who were overweight. In 2016, an additional study in the city of Lausanne
found that, even adjusting BMI values for other socio-economic criteria
such as educational level, age, state of health, ethnic origin, gender
and alcohol consumption, overweight people were clearly concentrated in
the west of Lausanne.
Four deprivation factors tested
Stéphane
Joost used the same indicator – the Townsend Deprivation Index (TDI) –
for this study as the British research. The index was developed in 1987
and can be used to create a map of a city based on four factors:
unemployment rate, household overcrowding (i.e. the relationship between
the number of inhabitants and the number of rooms per dwelling), and
the proportion of car owners and home owners. These last two factors are
now questionable, since the fact of not owning a car in a city centre
is not necessarily an indicator of deprivation. In the map of Lausanne,
for example, the TDI is overestimated in central districts of the city.
Nonetheless, the capital of Vaud appears divided, with a higher
deprivation index in the west than the east.
Stéphane
Joost then sent these data to researchers at the CHUV. The researchers
calculated the degree of interaction between the TDI and a genetic risk
score (GRS) influencing body mass index. The GRS is a combination of 69
genetic variants creating a predisposition to obesity. The result that
emerged was a disparity between the east and west of the city. This is
difficult to quantify precisely, however, because of the small cohort
size (6,000 individuals). By comparison, the participants in the British
study, which included 10 additional genetic variants predisposing an
individual to obesity, put on an average of one additional kilo (3.6
kilos compared with 2.8 kilos for a person of average height) when they
lived in an environment at high risk of deprivation.
Better targetting prevention measures
“Our
study shows that it is not enough to target prevention measures for
weight gain on specific factors such as consuming sugary drinks or fried
foods, when disadvantageous socioeconomic conditions accentuate a
genetic predisposition to obesity. We therefore need to ask to what
extent changing spatial planning could be a means of containing the
current obesity epidemic,” explains Stéphane Joost. There is no shortage
of hypotheses in this area. As well as having more green space and
wooded areas than the west of the city, districts in the east are
thought to be less affected by night-time noise, mainly linked to road
and rail traffic.
The analysis from
the CHUV is the same: “Obesity is caused by multiple factors. We focused
here on calculating the impact of the deprivation factor on the genetic
predisposition to obesity. Our study shows that it is very difficult to
specify which environmental and lifestyle factors are the most
critical, but that there is an interaction between the risk of becoming
overweight for people who have a genetic predisposition to it and the
socio-economic conditions reflected by the type of district they live
in. From our perspective, it’s quite an unfair factor,” comments Zoltán
Kutalik, a statistician specialising in genetics.
Multiple solutions
What
solutions would the researchers suggest to address this inequality?
“Improve the level of education among the population, encourage the
award of study grants and offer gym memberships... These measures would
have an impact on residents’ genetic predisposition to obesity,”
suggests Zoltán Kutalik. According to Stéphane Joost, work on urban
planning is another avenue to explore. “Limiting night-time traffic on
busy roads, better sound insulation for buildings, making certain
districts less cut-off than they currently are, more direct access to
sociocultural and sporting facilities and developing environmentally
friendly transport could also reduce exposure to obesity and limit the
divide between the west of Lausanne and the rest of the city.” The next
stage of the CHUV and EPFL research will focus on examining these
hypotheses.
References