What would be the effective reproduction number (R) of unhealthy lifestyle behaviours?
In their editorial the authors describe the similarities between COVID-19 and non-communicable diseases (NCD’s) and call both “socially transmitted conditions” . The authors mention important factors behind the pandemics of NCDs, such as poverty, poor education, inadequate housing and the influence of the tobacco, alcohol and processed food industries. However, the authors fail to define why these NCDs are socially transmitted conditions. We believe that a better understanding and recognition of the social contagiousness of unhealthy lifestyle behaviour is crucial to decrease the prevalence of these behaviours and the related NCD pandemics. People are not born to behave unhealthily, but learn to, how to and when to do it from others who already do it, including family members and peers. The social contagiousness of unhealthy behaviour is, however, known to go far beyond two directly connected friends or family members .
If smoking, drinking alcohol, and eating unhealthy food are indeed socially contagious and if we compare it to the spreading of infectious diseases like COVID-19, it is interesting to know what the ‘effective reproduction number’ (R) would be. The R is used to measure the spreading capacity of an infectious disease as COVID-19. It stands for the average number of individuals that one infected person will spread the virus to at a given time in a certain population. The level of R varies in time and can be influenced by measures, such as social distancing and isolating infected individuals. To reduce the NDC pandemics it could be important to express the transmission of these unhealthy behaviours in a transmission coefficient, such as R. It is known that within families the intergenerational transmission of these unhealthy behaviours is relatively large. For instance, children of smoking parents have a 2 to 3 times higher chance of becoming a smoker themselves. How would this translate in a transmission coefficient R?
During the past decades the number of smokers in The Netherlands has decreased very slowly. At this moment about 3 million people in our country smoke and about 27.000 teenagers start to smoke every year. On the back of an envelope, one could say that the national R for smoking in the Netherlands in the past years is about 0.009. This indicates that a transmission factor far lower than 1 is sufficient to keep the pandemic of smoking going. Most likely the transmission coefficient R varies between different social networks, subgroups of different socioeconomic status or between large city or rural areas. This observation would translate into another R of a specific unhealthy lifestyle factor in specific groups at a given time. Detailed knowledge of the landscape of transmission and specific effects of different unhealthy lifestyle behaviours in specific ecosystems or countries could be of great help to disrupt the transmission of unhealthy behaviour and stem the tide of pandemics like that of obesity, smoking, diabetes, and alcohol use.
1. Sheldon TA, Wright J. Twin epidemics of covid-19 and non-communicable disease. BMJ 2020; 369:m2618 doi: https://doi.org/10.1136/bmj.m2618
2. Christakis N, Fowler J. Connected. The amazing power of social networks and how they shape our lives. London: Harper Press: 2010.
Competing interests: No competing interests