Asthma is a condition characterised by constriction in the airways of the lungs. Inflammation in the airways is another common feature, and this may also be accompanied by the presence of some mucus that can obviously add to the obstruction of airflow in and out of the lungs. Common symptoms of active asthma include shortness of breath, wheezing and coughing.

There are many potential triggers for asthma. Some of these can come from within the body (e.g. food), while others can come from the outside. Outside triggers include ‘airborne’ agents such as pollen, mold spores, pollution, and the faeces of the house dust mite.

I was interested to read about a nutritionally oriented approach that was tried in a group of house dust mite-sensitive asthmatics. The treatment under test was a blend of omega-3 fats at a dose of 0.6 g per day. The study lasted just 5 weeks. In the last two weeks of the study, the participants were challenged each day with house dust mite ‘allergen’.

The study participants were monitored with a number of tests including the amount of the gas nitric oxide they exhaled. This test provides an indirect measure of the amount of inflammation in the airways. Despite the relatively low dose of omega-3 used in this study and quite short duration, the active treatment (compared to placebo) led to significantly lower levels of exhaled nitric oxide. In other words, taking omega-3 appeared to reduced inflammation in the lungs of these asthmatics. This is consistent with prior knowledge that we have regarding omega-3 fats in relation to their natural anti-inflammatory properties.

Allergic reactions to house dust mite faeces (or other allergens) typically involve white blood cells known eosinophils. Eosinophil counts in the blood generally go up during allergic responses in the body. The researchers found that eosinophil counts were lower in those taking the omgea-3 supplement compared to those taking placebo. Other markers of disease activity were lower also.

What this study suggests is that omega-3 supplementation may be beneficial for asthmatics, particularly those suffering from allergic asthma.

While interesting and relevant, I think, what this study does not tell us is if omega-3 supplementation actually helped the symptoms of the asthmatics being tested. However, there has previously some work that suggests omega-3 supplementation may help in this regard. In a study published in 2000, asthmatic children were treated with a mix of EPA and DHA (two omega-3 fats found in oily fish) or placebo (olive oil) for a period of 10 months. The total daily dose of omega-3 fats was in the order of 30 mg per kg per day.

Omega-3 supplementation led to a significant reduction in asthma symptom scores. This study provides at least some evidence that omega-3 supplementation has the potential to control asthma.

References:

1. Schubert R, et al. Effect of n-3 Polyunsaturated Fatty Acids in Asthma after Low-Dose Allergen Challenge. Int Arch Allergy Immunol 2008;148(4):321-329.

2. Nagakura et al. Dietary supplementation with fish oil rich in omega-3 polyunsaturated fatty acids in children with bronchial asthma. Eur Resp J. 2000;16(5):861-865.

Accumulated weight around the mid-riff (abdominal fat) is associated with an increased risk of chronic conditions including cardiovascular disease and type 2 diabetes. One of the mechanisms that may cause the build-up of fat around the middle concerns secretion of the hormone insulin, which is produced principally in response to rising levels of sugar in the bloodstream that come from consuming carbohydrate in the diet. Carbohydrates that are most disruptive in terms of blood sugar (high glycaemic index/load carbohydrates) are the ones most likely to cause surges of insulin that can cause people to pile on the pounds around the middle. I don’t suppose it’s any surprise therefore that these carbs are also associated with an increased risk of cardiovascular disease and type 2 diabetes (see here and here).

However, the biochemical disruption wreaked by blood sugar-destabilising carbohydrates has been linked with an increased risk of other conditions too. For example, the second link above goes to a discussion of the study which finds and association between high GI and/or GL diets and increased risk of gallbladder disease and breast cancer. In recent times, evidence has also linked disruptive carbohydrates with an increased risk of age-related macular degeneration (AMD) – the most common cause of loss of vision and blindness in adults. See here and here for the details of two relevant studies.

Bearing all these strands of evidence in mind, then one would predict that the extent of abdominal fat would have some association with risk of AMD. A study published this month in the Archives of Ophthalmology examined the association between changes in the waist-to-hip ratio (a measure of abdominal obesity) and risk of AMD in middle-aged men and women over more than 6 years [1]. At the end of study, higher waist-to-hip ratio (WHR) was associated with elevated risk of AMD. What was also interesting is that individuals who saw a decrease in their WHR generally saw a reduction in risk of AMD too. Overall, a 3 per cent or more decrease in WHR was associated with a 29 per cent reduced risk of AMD.

The authors of this study went further by sub-dividing the study population in individuals of ‘healthy’, ‘overweight’ and ‘obese’ weight categories. The reduction in risk of AMD coming with reduced WHR was only seen in individuals in the obese category (BMI 30 or more). In these individuals, a 3 per cent or more reduction in WHR ratio was associated with a 59 per cent reduced risk of AMD.

Epidemiological studies like this one cannot be used to conclude that losing weight around the middle helps protect against AMD. However, the consumption of high GI/GL foods is associated with AMD, and eating of less of them may reduce the risk of AMD. A diet lower in disruptive carbs generally helps trim the waist too. Put all this together, and I reckon there’s a good argument for the notion that eating a diet low in blood sugar disruptive carbohydrates may help individuals preserve their vision in later life.

References:

1. Peeters A, et al. Changes in Abdominal Obesity and Age-Related Macular Degeneration: The Atherosclerosis Risk in Communities Study Arch Ophthalmol. 2008;126(11):1554-1560