A nutritious diet is healthy for everyone – including people with asthma. So far, no one has been able to find a nutrient supplement or specific food that can make asthma better. Nevertheless, several observational studies show that eating nutrient-rich foods is linked with lower rates of asthma, less wheezing, and less severe asthma.1,2
In general, it is hard to study diet. The nutrients in whole foods are far more complicated than supplements. Therefore, studies of nutrient supplements may not be enough to know whether certain kinds of food are helpful. It is also difficult to studying dietary patterns, because it is hard to measure what people eat. It is challenging to compare studies that measure diet and report results in different ways.
Nevertheless, there is little risk that eating a healthy, balanced diet will make asthma worse!
Will eating more antioxidants help my asthma?
Vitamins A, C, E, and selenium are antioxidants. Antioxidants help to reduce tissue damage and airway inflammation. They help the immune system to function normally.1
Good sources of antioxidants are:1
- Vitamin A: Orange-yellow fruits and vegetables, whole milk, liver, eggs.
- Vitamin C: Wide variety of fruits and vegetables.
- Vitamin E: Nuts, seeds, green vegetables, vegetable oils.
- Selenium: Meat, fish, eggs, seeds, Brazil nuts, beans, grains.
People with asthma tend to have lower blood levels of antioxidants.2 Observational studies show that lower antioxidant levels are linked to lower lung function in adults. They are also linked to increased risk of asthma in adults and children.2 Unfortunately, observational studies have a number of limitations. A serious limitation is that it is not possible to tell which factor caused the other. Do people with lower blood antioxidant levels develop asthma? Or do people with asthma have lower blood antioxidant levels because of the stress of asthma on their body? Do people eat less nutrient-rich foods because they have asthma? Or do they have asthma because their diet is low in antioxidants?
To clarify the link seen between antioxidants and asthma, researchers have done interventional studies. A typical design for these studies is that half the participants get a nutrient supplement and half get a fake treatment (placebo). This is called a randomized controlled trial. If the people who get the supplement improve, then it is fair to say that the supplement caused the improvement. Unfortunately, studies of vitamin C and selenium supplements have not been successful.2 Studies of vitamin E supplements have produced inconsistent results. Two studies showed no benefit of vitamin E. Four others showed that vitamin E made the airways less sensitive to ozone.1
Will eating more omega-3 fats help my asthma?
Omega-3 fats are anti-inflammatory.3 Asthma is an inflammatory condition. Therefore, one theory is that eating more omega-3 fats can be helpful for people with asthma.3 The typical Westernized diet is low in omega-3 fats.2 Good sources of omega-3 fats are oily fish (fresh tuna, herring, mackerel, trout, and salmon), canola and soybean oil, walnuts, and flaxseed.
The results of observational studies have not been consistent.2 A few observational studies have shown that people who eat more fish have a lower risk of asthma.2 However, other studies show that low intake of omega-3 fats might actually protect against asthma.4
Randomized controlled trials of fish oil supplements for asthma have been disappointing.2,4 One exception might be using them to treat exercise-induced asthma. Two high-quality studies showed that fish-oil supplements improved lung function and reduced inflammation in elite athletes.2,4
Will increasing my vitamin D levels help my asthma?
Low vitamin D levels in the blood have been linked with airway sensitivity, lower lung function, more asthma attacks.5 People with low vitamin D levels are less responsive to asthma medications. One theory is that vitamin D makes inhaled corticosteroids work better. Another theory is that low vitamin D levels increase inflammation. Your body makes vitamin D when your skin is exposed to sunlight. Milk, ready-to-eat cereals, and some types of orange juice are fortified with vitamin D. Oily fish (salmon, tuna, and mackerel) and egg yolks also have vitamin D.
One large, randomized trial was designed to see if taking a vitamin D supplement would make asthma medications more effective.5 More than 400 people with asthma and low vitamin D levels took part in the study. However, taking vitamin D did not improve asthma treatment.
Can losing weight improve my asthma?
Research suggests that there is a link between being overweight and having asthma.6 Extra body weight changes the immune system, the inflammatory signals in the body, and the way the lungs function.7,8 One study showed that 5% weight loss is enough to improve asthma control.7
Are there foods that make my asthma worse?
Food allergens are rarely triggers for asthma.8 There is no general recommendation to avoid certain foods because of asthma. A few people with asthma react to sulfites, which are food preservatives found in wine, beer, potatoes, shrimp, and dried fruit. If you react to sulfites or have food allergies, it is important to avoid the foods that you are allergic to.