Colouring in dog food

There seems to be a lack of scientific research into the subject of food colouring, present in most commercial dog foods, and any link to unwanted canine behaviour. There are however anecdotal reports where removal of food additives have resulted in an improvement in a dog’s behaviour.

At a neurobiological level additives are broken down in the intestine and carried through the bloodstream to the brain, where they can affect brain chemistry in a variety of different ways. Brown (2003) suggests that in particular petroleum-based dyes, such as tartrazine and erythrosine can act within the brain just like neurotransmitters; these fake neurotransmitters bind to receptors within nerves and deliver what Brown terms as “a false signal” resulting in unwanted firing within these nerves, and potential issues such as overactivity, aggression, and issues such as poor coordination and poor impulse control. 

Ward’s (1997) findings that synthetic food colourings in particular lead to attention deficit hyperactive disorder (ADHD) in children through the mechanism that Brown suggests, further supports Brown’s argument for food colouring as a potential “false” neurotransmitter. Ward suggested the reason for increased ADHD in children was linked to Zinc and or Iron deficiency, and that this in turn leads to elevated levels of copper within the blood, which in humans has been linked to periods of violence, learning disability, depression and hyperactivity. Toren et al (1996) also point out that Zinc deficiency reduces the production of melatonin and serotonin and that this reduction “could plausibly contribute to the kinds of behavioural disturbances found in children with ADHD”. 

Both Brown and Ward suggest that because nerves (together with the endocrine system) control almost all bodily functions, then small disturbances in nerve transmissions can affect behaviour; there is however little evidence to show what is a safe level of artificial colouring.

Silbergeld’s (1982) research into artificial colourings and behavioural change found that erythrosin and tartrazine inhibited the uptake of neurotransmitters and precursors and in particular affected the levels of sodium, potassium and ATP in the brain, and that this reduction affected the ability of nerve terminals to take up and retain dopamine.

The European food safety authority conducted a study in 2011 looking at the safety of erythrosine, which is commonly used in cat and dog food, their findings show that erythrosine contains 56% iodine and that this high level of iodine can affect thyroid function, and in turn metabolism and behaviour, they also note that most commercial pet food manufacturers used up to 500 mg per kilogram (complete feed) and that this amount is excessive and should be reduced to no more than 18 mg per kilogram (complete feed) for dog and cat food; they note that research shows that excessive levels have led to allergy type symptoms, but they make no note of its effect on behaviour, other than to say that rats showed symptoms suggestive of an ADHD type disorder when fed the equivalent of 500 mg per kilogram.

So if artificial colours are so bad why are they in dog food? I believe there are several reasons, firstly while there is a substantial body of evidence that hyperactivity in children and ingesting food colourings are linked, not all authorities agree; and while veterinarians suggest they have seen “substantial rises in … behavioural issues linked to artificial additives” (Daily Mail 2008), artificial colouring (along with other artificial additives) remain legal and there is no empirical evidence to support their removal.  

Secondly as consumers, we feel a need to have enticing looking food, because as a species humans rely on the look of food to tell us whether it is appetizing, and we believe this applies to our dogs. Visual enhancement of dog food can be achieved by both natural and artificial colouring (we only have to look at the likes of Beneful www.beneful.com to see the visual effects of colouring); our dogs however have little interest in the colour of the food as they rely much more on olfactory and palatability factors than foods visual appearance (Lindsay 2000). 

And lastly the vast majority of research into commercial pet food is carried out by the pet food manufacturers, through its various worldwide pet food manufacturers associations. So we could argue there is a conflict of interest between profitability (through the sale of manufactured pet food) and the health of the animals concerned.  The Pet Food Manufacturers' Association suggests there is no evidence that additives in pet food cause behavioural problems in dogs. They state:

"The use of additives in pet food is strictly regulated by the EU, the authorisation process is rigorous and pet food additives are regularly reviewed to ensure safety… Consumers want reassurance on additives, but not full listing… There is no peer-reviewed scientific evidence currently available, or that we are aware of, to suggest a link between behavioural problems in pets and additives in pet food."  (PFMA 2014).

The debate on the use of food colourings is set to continue, and many colourings once deemed “safe” are now banned worldwide for human consumption, but a few still used for pet foods. A study being undertaken by veterinarians in the UK on the behavioural effect of food colouring using 300 dogs is underway and while this is only a small number of dogs it will hopefully set the benchmark for future studies, which may, or may not prove, that artificial food colourings in manufactured dog foods lead to problem behaviours. Until this study is completed it would seem reasonable that food colouring related behavioural issues affecting children, be used as a blueprint for the regulation of artificial colouring use in pet food.

 

References

Brown, L. (2003) Diet and Behaviour: first do no harm. Retrieved 22^nd of December 2013 from http://www.iwu,edu/-wellness/environment_folder/nehaviour_noharm.htm

Daily Mail (2008) Vet’s warning over additives in food which could put your pet at risk. Retrieved 22^nd of December 2013 from http://www.dailymail.co.uk/news/article-1051189/Vets-warning-additives-food-pets-risk.html

European food safety authority (2011). Scientific opinion on the safety and efficacy of erythrosine in feed for cats and dogs. Retrieved 3^rd of January 2014 from http://www.efsa.europa.eu/en/efsajournal/pub/2447.htm

Lindsay, S.R. (2000) Handbook of applied dog behaviour and training volume 1. Blackwell publishing. Iowa.

PFMA (2013). Prepared pet foods deliver optimum nutrition. Retrieved 12^th of December 2013 from http://www.pfma.org.uk/news/press-releases/prepared-pet-foods.cfm

Toren, P., Eldar, S., Sela, B.A., Wolmer, L., Weitz, R., Inbar, D., Koren, S., Reiss, A., Weizman, R., Laor, N. (1996) zinc deficiency in attention deficit hyperactivity disorder. Retrieved 10^th of December 2013 from http://www.fabresearch.org/423

Ward, N.I. (1997) Assessment of clinical factors in relation to child hyperactivity. Retrieved 22^nd of December 2013 from http://hriptc.org/zinc_defficiency.html