Childhood obesity is a major and increasing public health concern, with prevalence in the UK rising rapidly in children as young as 3 years (Buchan et al., 2007; Bundred et al., 2001). Some risk factors associated with childhood obesity include parental obesity, maternal smoking, increasing birth weight, and a positive mismatch between energy intake and energy expenditure (Prentice & Jebb, 1995; Reilly et al., 2005). Similarly, the incidence of obesity in companion pets is also thought to be increasing (German, 2006), and is known to have detrimental effects on pet health and longevity (Kealy et al., 2002; Lund et al., 2006). Furthermore, there is emerging evidence of a possible link between human and companion animal obesity, since overweight owners are more likely to own overweight dogs (Holmes et al, 2007). Given that the prevalence of childhood obesity is greater in families where mothers are heavier (Hawkins & Law 2006), there may be close associations between the causes of obesity in both children and companion animals. This is, perhaps, not surprising since the owner-pet relationship is similar to that between parent and child (Berryman et al., 1985). Given such associations, it is likely a major cause of human and companion animal obesity is the fact that all family members (including pets) are exposed to common environmental factors, namely the 'family food environment' (Campbell & Crawford 2001), which may predispose to obesity.

Half of UK households own a pet of some type, with one in four owning a dog( Anon, 2004; Westgarth et al., 2007). In a community-based study of 1278 households, we have identified a number of factors that are associated with households that choose to own dogs, including families with school age children being more likely to own a dog (Westgarth et al., 2007a). The beneficial impact of companion animal ownership on the physical, social and psychological health of people has been well documented (Friedmann, 1995; Headey, 2003; Katcher, 1981; Katcher & Friedmann, 1982; McNicholas et al., 2005). However, although there is some evidence of a link between obesity in dogs and their owners, there has been no specific research into a possible association between pet ownership and childhood obesity.

In the light of the increasing childhood obesity epidemic across western societies, and failure of measures taken so far to control this, new intervention means are urgently required. Intervention may also have implication for the pet population; given the suggested links between obesity in humans and companion animals, interventions can be adopted which tackle both problems concurrently. Indeed it is possible that pet ownership, and in particular dogs, may reduce the risk of childhood obesity. This may be through exercise and lifestyle factors, or some other measure associated with the types of families that choose to own dogs/pets. In fact, a previous study has demonstrated the effectiveness of a combined weight loss programme, for owners and pets, and suggested that social support for human weight loss in family members should be extended to include pets (Kushner et al., 2006).

The null hypothesis to be tested using ALSPAC data is that pet ownership has no association with childhood obesity. In order to investigate this a number of strategies will be used, including investigation of ALSPAC data of children of 7yrs. On discussion with the ALSPAC group and subject to there being appropriate data, the investigation may also be conducted in a longitudinal manner, using pet ownership and BMI at different ages of the child. This may provide additional insight into direction of causality.

Variables requested will be similar to this paper

Reilly, J. J., Armstrong, J., Dorosty, A. R., Emmett, P. M., Ness, A., Rogers, I., Steer, C. & Sherriff, A. (2005). Early life risk factors for obesity in childhood: cohort study. Bmj 330, 1357.

As this paper only includes risk factors before 3yrs (but an outcome of obesity at 7yrs), other useful variables may be identified up to the age 7yrs, on discussion with the ALSPAC group.

Pet ownership variables are also requested, including during pregnancy and each year, in addition to contact with animals, those years that these questions were asked. All data was collected using questionnaires unless otherwise stated. Pet ownership and contact with animals will be investigated as a whole and for individual species types.

BMI, child, 7yrs (and possibly yearly).

Pet ownership, mother/principal carer, pregnancy to 7 years.

Contact with animals (at least once a week at home or elsewhere), for child, 15, 24, 38 and 54 months.

Maternal social class (SES), mother, 32 weeks gestation.

Maternal education, mother, 32 weeks gestation.

Ethnicity, child, birth.

Energy Intake of Child, child, food frequency questionnaire at 30 months.

Birth weight, child, birth, delivery room.

Sex, child, medical records.

Maternal parity, mother, questionnaire 18 weeks gestation.

Maternal smoking during pregnancy, mother, 32 weeks gestation.

Season of birth, child, medical records.

Gestational age, child.

Number of foetuses, child, medical record.

Breast feeding, child, 6 months questionnaire.

Age at introduction of complementary feeding, child, 6 months questionnaire.

Parents body mass index, mother, prepregnancy.

Parents body mass index, father, prepregnancy.

Number of siblings, child, 18 months.

Ethnicity of child, child, 32 weeks gestation.

Age of mother at delivery, mother, birth, clinical records.

Time spent watching tv per week, child, 38 months.

Time in car on weekdays per day, child, 38 months.

Time in car on weekend days per day, child, 38 months.

Duration of nighttime sleep, child, 38 months.

Dietary patterns (food frequency questionnaire), child, 38 months.

A range of studies have now demonstrated human health benefits from pets. However, the vast majority of this work has used samples of Caucasian origin. Where non-Caucasian owners have been included, they have been in numbers too low to draw conclusions about differences in pet ownership across ethnic groups. It is important to look at patterns of pet ownership across ethnic groups to understand differences in attitudes and behaviour toward pets. Significance of the relationship with pets, levels of attachment and patterns of activity with pets may all vary so that ethnic groups may differ in potential benefits from pet ownership. The ALSPAC data may provide us with some insights to ethnic differences in pet ownership within the UK.

The University of Liverpool is an appropriate institution to be conducting this study, due to its international reputation, in both medical and veterinary fields, for obesity research and track record of collaboration. Comparative obesity research is actively encouraged and co-ordinated through the Liverpool Obesity research Network (LORN), which arranges regular meetings and discussion on all aspects of obesity research. Previous collaborations between the Faculties of Veterinary Science and Medicine have been highly successful, for instance, leading to the foundation of Europe's' first weight management referral clinic for companion animals (www.pet-slimmers.com), funded by WALTHAM. Dr Peter Bundred is an acknowledged expert in the field of childhood obesity epidemiology, and has published widely in this area. Therefore, he is accustomed to the procedures necessary for undertaking such research. Dr Alex German is an RCVS-recognised specialist in internal medicine whose main research focuses is in companion animal obesity biology, and who already collaborates with WALTHAM in this area. Dr Carri Westgarth is experienced in investigating factors associated with pet ownership and the characteristics of human-dog interactions.

The science is novel and of high priority, given that it targets the most important medical disease in humans and companion animals and given current estimates on obesity prevalence. The information gained will significantly increase the understanding of beneficial or other associations between pet ownership and childhood obesity, and be the first step towards developing effective strategies to improve obesity management.

Anon (2004). Pet ownership trends. Pet Food Manufacturers Association

Available at http://wwwpfmacom/public/petownershiphtm.

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Buchan, I. E., Bundred, P. E., Kitchiner, D. J. & Cole, T. J. (2007). Body mass index has risen more steeply in tall than in short 3-year olds: serial cross-sectional surveys 1988-2003. Int J Obes (Lond) 31, 23-29.

Bundred, P., Kitchiner, D. & Buchan, I. (2001). Prevalence of overweight and obese children between 1989 and 1998: population based series of cross sectional studies. Bmj 322, 326-328.

Campbell K & Crawford D (2001). Family food environments as determinants of pre-school aged children's eating behaviours: implications for obesity prevention strategies. Australian Journal of Nutrition and Dietetics 58, 19-25.

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Headey, B. (2003). Pet ownership: good for health? Medical Journal Of Australia 179, 460-461.

Holmes, K.L., Morris, P.J., Abdulla, Z., Hackett, R. & Rawlings, J.M. (2006) Risk factors associated with excess body weight in dogs in the UK. Journal of Animal Physiology and Animal Nutrition 91, 166-167.

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Lund, E. M., Armstrong, P. A., Kirk, G. A. & Klausner, J. S. (2006). Prevalence and risk factors for obesity in adult dogs from private US veterinary practices. International Journal of Applied Research in Veterinary Medicine, 177-186.

McNicholas, J., Gilbey, A., Rennie, A., Ahmedzai, S., Dono, J.-A. & Ormerod, E. (2005). Pet ownership and human health: a brief review of evidence and issues. BMJ 331, 1252-1254.

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Westgarth, C., Pinchbeck, G. L., Bradshaw, J. W., Dawson, S., Gaskell, R. M. & Christley, R. M. (2007). Factors associated with dog ownership and contact with dogs in a UK community. BMC Vet Res 3, 5.