It is widely acknowledged that unhealthy diets and obesity are risk factors linked to the development of non-communicable diseases such as type 2 diabetes, cancer and cardiovascular disease.
But the consequence of a diet that is deficient in nutrients also has less well-known health implications. Poor diets that result in nutrient deficiencies – but do not necessarily lead to an abnormal body mass index – can have profound consequences for the functioning of our nervous systems, particularly vision. However, this issue has remained ‘under the radar’ of many health professionals, according to Dr Denize Atan of the University of Bristol.
“Micronutrient deficiencies may occur due to malabsorption, drug interactions or inadequate dietary intake. In developed countries, purely dietary causes of micronutrient deficiencies do not have to be associated with inadequate energy intake or low BMI – so-called “hidden hunger”. This means that they are not often high on the radar of health professionals and so we probably underestimate their prevalence,” she told FoodNavigator.
Dr Atan is one of the authors of a new research paper examining the link between diet and vision. Published in the Annals of International Medicine, the research examined the link between poor nutrition and permanent damage to the nervous system.
According to the authors, nutritional optic neuropathy should be considered in any patient with unexplained vision symptoms and poor diet, regardless of BMI.
Nutritional optic neuropathy is a dysfunction of the optic nerve usually caused by malabsorption, drugs, or poor diet combined with alcoholism and/or smoking. The condition is potentially reversible if caught early. But if left untreated, it leads to permanent blindness.
Case study: When ‘fussy eating’ ends in blindness
Researchers from Bristol Eye Hospital in the UK reported the case of a 14-year-old patient who first visited his GP complaining of tiredness.
The boy was described as a ‘fussy eater’ but had a normal BMI and was not taking any medication. Tests showed macrocytic anemia and low vitamin B12 levels, which were treated with vitamin B12 injections and dietary advice.
By age 15 years, the patient had developed sensorineural hearing loss and vision symptoms, but no cause was found. By age 17, the patient’s vision had become progressively worse, to the point of blindness.
When the patient’s nutrition was investigated, physicians found vitamin B12 deficiency, low copper and selenium levels, a high zinc level, and markedly reduced vitamin D level and bone mineral density.
The patient revealed that he had subsided on a diet of French fries, Pringles, white bread, processed ham slices and sausages since he was elementary school age.
By the time his condition was diagnosed, the patient had permanently impaired vision.
“In this case study, the subject had an extreme form of picky eating,” Dr Atan noted. “He did not eat a varied diet and restricted his food intake to what most people would call junk food - chips and crisps are both potato based, and sausage/ham are both processed forms of pork so he was essentially eating only two types of food. Perhaps if he'd only eaten fish and veg, he wouldn't have run into problems. Nevertheless, he was still consuming enough calories that he had normal height and weight and did not look overtly malnourished.”
According to Dr Atan the case highlights that this behaviour can become ‘entrenched’ and that many people who choose to eat restricted diets do not realise the implications this could have for their health.
“The case highlights that fact that picky eating can become an entrenched behaviour if it is not addressed early enough. Moreover, there are many people who choose to eat chips and crisps all the time - not because they are picky eaters but because they prefer these food types - and are not aware that this type of diet could affect their vision.”
Micronutrient deficiencies – more common than you’d think
Dr Atan said that, while nutritional optic neuropathy is rare in developed countries, micronutrient deficiencies and under-nutrition is a relatively widespread problem.
“Micronutrient deficiencies are common, affecting an estimated two billion people worldwide. In low- and middle-income countries, poverty and inadequate food intake are the main causes of micronutrient deficiencies, but micronutrient deficiencies also exist in high-income countries like the UK.
“For example, iron deficiency affects 2-5% of adult men and postmenopausal women, vitamin B12 deficiency affects 6% of the population over 65 years, and severe vitamin D deficiency affects 16% of middle aged adults in winter and spring in the UK. In low-income countries, vitamin A deficiency is the most common micronutrient deficiency and the most common cause of blindness worldwide but folate and iron deficiency are also common worldwide. All of the above vitamin deficiencies can affect vision.”
Dr Atan believes that there is an education piece around the need to communicate the risks of under-nutrition and the link to impaired vision. She is currently working on a proposal to raise awareness among regulators, consumers and medical professionals.
She has also seen a move toward fortification as a tool to address common nutrient deficiencies at a population level. “There is a drive to fortify more foods with vitamins in the UK - for example vitamin D in cereals and more recently, the government has begun open consultation on whether we should add folate to flour.”
Annals of International Medicine
Published online ahead of print
Authors: Dr Denize Atan,