Summary of findings

This study is the first, to the knowledge of the authors, to investigate the effects of the neighbourhood food environment on bone mass in children from birth to 6 years of age. Our results showed that greater access to fast-food outlets within residential neighbourhoods was associated with lower BMC adjusted for bone area in infancy and remained robust after adjustment for confounding factors. There were no significant associations between fast-food outlet exposure and bone measures at 4 or 6 years of age. We also found that that greater access to healthy speciality stores within residential neighbourhood, such as greengrocers, farm shops and butchers, was associated with higher BMD at 4 and 6 years of age. Findings for BMC were similar after adjustment for bone area and confounding factors at 4 years, though attenuated after adjustment at 6 years. The direction and effect sizes of these relationships between bone growth measures and count of fast-food outlets and healthy speciality stores were largely consistent between children who had not moved neighbourhood since their mothers completed the initial survey and the total sample. There was little evidence that exposure to supermarkets within a child’s home neighbourhood related to their bone mass or density.

Comparison with previous research

Previous research examining the effects of the local food environment on health has largely focused on weight or dietary outcomes. Research in Australia identified no association between fruit and vegetable intake of children and the number of greengrocers within 800 m radius of residential address [28]. Our study showed that a greater count of healthier specialty stores, such as greengrocers, farm shops and butchers, within residential neighbourhood was positively associated with child bone health. The Australian study also showed no relationship between supermarket accessibility in home neighbourhood and fruit and vegetable intake. Similarly, numbers of grocery stores per capita were not associated with changes in weight status of primary school children in the USA [29]. The lack of evidence for an effect of supermarket and grocery store accessibility on weight and dietary outcomes is consistent with the lack of an association between supermarket access and bone outcome measures in our study. The large variety of both healthy fresh produce and unhealthy processed food products on sale in supermarkets suggests that they can be classified as neither healthy nor unhealthy [1]. The healthy and unhealthy effects that supermarkets can have on dietary outcomes were illustrated in previous UK research which measured supermarket density per square kilometre within an 800-m radius of home [30]. The findings of that study showed that greater density of supermarkets was associated with higher vegetable consumption but also higher intakes of sweets, sugary drinks and white bread.

More recent research in the UK examined the relationship between weight measures from the English National Child Monitoring Programme in relation to food outlet counts within Middle Super Output Areas (MSOA). MSOAs are similar to but larger than LSOAs and have a population density of approximately 7500 compared to 1500 of LSOAs. Findings showed that greater combined counts of greengrocers, butchers, supermarkets, cafes and restaurants were associated with lower rates of overweight and obesity in children aged 4 to 5 years [5], although this relationship was not significant among children aged 10 to 11 years. Greater exposure to fast-food outlets was, however, associated with increased prevalence of overweight and obesity among the older children, but the opposite relationship was observed for fast-food outlet exposure among the younger children. In the present study, we also found that the relationship between the local food environment and bone density differed across age groups. The strongest relationship between greater fast-food exposure and lower bone density was observed in infancy, whereas relationships between greater exposure to healthy specialty stores and bone density were seen at 4 and 6 years of age.

There are a number of ways in which the neighbourhood food environment might influence bone development during childhood. Previous research has demonstrated that the quality of maternal diet during pregnancy is associated with childhood bone development such that children of mothers with better dietary quality have higher bone density at 9 years of age [15]. The findings of the current study suggest that, during the preconceptional period, poorer access to fast-food outlets and greater access to healthy specialty stores related to higher bone density at birth and during childhood. Thus, exposure to a more healthy food environment might optimise childhood bone development through its influence on maternal dietary quality. It is also possible that the local food environment contributes to dietary choices during childhood. A healthy diet during childhood, with adequate protein, calcium, vitamin D, fruits and vegetables, has a positive influence on bone health [13]. Mothers exposed to less healthy food environments might find it difficult to access healthy foods for their children and this in turn could lead to lead to less optimal bone development.

Strengths and limitations

A strength of this study was the consideration of both healthy and less healthy types of food outlets, and the finding that these outlets have opposing associations on measures of bone growth. Another strength was the use of DXA which allowed detailed assessment of bone outcome measures. The sensitivity analysis comparing families that had moved home since the initial interview and the total sample demonstrated similar trends between groups. However, the small sample size of the group who had not moved neighbourhood was a drawback that meant that, although many of the effect sizes of these relationships appeared similar, they were not statistically significant.

The use of LSOA boundaries as the area measure of residential neighbourhood is a limitation of this study. Administrative boundaries such as LSOAs and census tracts are unlikely to be entirely accurate in representing an individual’s unique spatial experience [31]. Uniform representation of environmental exposures is provided for individuals whether they reside near the centre or the boundary, and natural boundaries such as railway lines in adjacent units are not considered [32]. In addition, this study considered exposure to the neighbourhood food environment but did not have sufficient data to allow consideration of the influence of food outlets to which mothers and children may have been exposed during their daily activities such as when they are en route to school or childcare [33–35]. These limitations of using LSOA areas may have contributed to the large number of neighbourhoods within our study that had no supermarket, healthy specialty store or fast-food outlet. However, associations between food outlets access and bone health were observed in this study. Further research will use the SWS participant data to examine how food outlet density in buffer zones around school and home are associated with body composition in primary school-aged children. The body composition and food outlet data were collected at different time points, and it is possible that the spread of food outlets may have changed from the time the women and children were surveyed. This is a common consideration in food environment research [36] and was somewhat accounted for by considering the differences in exposure–outcome associations between children who had moved neighbourhood since the initial survey was completed and those who had not. We did not examine change in food environment exposures over time, and there is some evidence to suggest that food outlet locations do change [37].

Public health implications

There has been an increased recognition that local authorities can take action to improve food environments and support their communities to make healthier food choices. For example, Public Health England in collaboration with the Local Government Association has released guidance encouraging local authorities to take action where appropriate to limit the number of fast food and takeaway outlets within their boundaries (especially near schools) [38]. Some local authorities have already taken action in this area by introducing planning laws to ban outlets selling hot takeaway food within 400 m of schools as well as putting general restrictions on the clustering of takeaways [39]. With public health responsibilities devolved to local authorities, there is real potential for more local authorities to align public health priorities with other internal sectors such as urban planning. The results of this study provide some evidence to support the introduction of zoning policies to increase the number of healthier speciality retailers within neighbourhoods and to decrease the number of fast-food chains and takeaway outlets. Financial constraints may hinder the introduction of such policies; therefore, further evidence from observational, intervention or natural experiment research could help to support more widespread action by local authorities [40].

Conclusion

In conclusion, our findings suggest that the neighbourhood food environment that mothers and young children are exposed to relates to bone development during early childhood. If confirmed in further populations and in different settings, action to reduce access to fast-food outlets could have benefits for childhood health and development.