Asthma has become a worldwide epidemic, with more than 300 million people worldwide suffering from it, 25 million of them in the US and 5.4 million in the UK. Its incidence is now at the highest level ever, with one out of 10 Americans experiencing asthma at some time in their life.
We know that 50–80 per cent of all asthma cases are the result of allergies,1 and not only airborne allergies to such things as dust, mites, animal dander, mould and pollens, but also food allergies, which are involved in 10–50 per cent of cases.2
But over the past decade, scientists have been carefully researching the role of a variety of foods and supplements like antioxidants in preventing or controlling asthma. Their findings are nothing short of revelatory.
• People with asthma have lower levels of dietary antioxidants like vitamins A, C and E in their blood,3 and the level of deficiency of these vital nutrients corresponds to the severity of asthma. Those with more severe asthma have greater deficiencies than those with milder asthma.4
• People consuming diets rich in antioxidants from fruits and vegetables have a lower incidence of asthma compared with those eating a typical Western diet low in vegetables and fruit. A large Finnish study showed that the lower the dietary consumption of antioxidants called ‘flavonoids’, found in fruits and vegetables, the more likely the development and severity of asthma.5
It’s not yet clear whether this connection between an antioxidant-deficient diet and asthma happens because the oxidative stress of asthma destroys antioxidants (see box, page 59) or because asthmatics have less nutritionally sound diets to begin with. But either way, eating more foods with antioxidants may well be helpful for preventing or controlling your wheezing.
Eat your greens (and reds and oranges)
In an article published in The American Journal of Clinical Nutrition, Australian scientists divided a group of adults with asthma into two groups, giving one a high-antioxidant diet with five servings of vegetables and two servings of fruit a day, and the other a low-antioxidant diet containing no more than two servings of vegetables and one serving of fruit a day.
After two weeks, the people consuming the high-antioxidant diet showed better lung function on breathing tests than did those on the low-antioxidant diet. In fact, after 14 weeks, those on the low-antioxidant diet not only had poorer lung function, but also higher blood levels of C-reactive protein (CRP), an important marker of systemic inflammation.6
The Australian scientists then demonstrated that just adding tomato juice (about two glasses a day) to the low-antioxidant diet led to a reduction in lung inflammation among their test subjects.7 Tomatoes are an excellent dietary source of carotenoids and vitamin C, and the asthmatics who drank the tomato juice showed a decrease in levels of white blood cells in mucus compared with those eating just the low-antioxidant diet.
Tomato juice alone, however, did not improve airflow in the lungs. The whole-food, high-antioxidant diet was more effective than tomato juice for that purpose.
The right kind of vitamin E
Another possible asthma trigger is too much of one kind of vitamin E and not enough of another one. Vitamin E is probably the best-known dietary antioxidant. There are eight forms of vitamin E in nature, of which two predominate in human tissues: alpha-tocopherol and gamma-tocopherol.
Alpha- and gamma-tocopherol differ in the way they combat inflammation. In laboratory experiments with animals and humans, gamma-tocopherol was shown to have unique effects that can benefit acute inflammation caused by exposure to bacteria, smoke or ozone.8 Researchers at Northwestern University in Chicago demonstrated that gamma-tocopherol increases both bronchial hyperreactivity and the recruitment of inflammatory eosinophils (a type of white blood cell) into lung tissue, whereas alpha-tocopherol does
When another team of researchers at Northwestern studied 4,526 asthmatics, they found that higher blood levels of gamma-tocopherol were associated with poorer lung function, while higher levels of alpha-tocopherol were associated with improved lung function.10
They concluded that, in chronic allergic asthma, alpha-tocopherol is anti-inflammatory and blocks airway hyperactivity, whereas gamma-tocopherol is proinflammatory, increasing airway hyperactivity and even interfering with the beneficial effects of alpha-tocopherol.11
Several other studies found reduced levels of alpha-tocopherol in the blood
The Northwestern University researchers believe that the key has to do with the fact that these two forms of vitamin E have opposite effects on the enzyme PKCα (protein kinase C alpha), which transports inflammatory cells into tissues during inflammation.13 PKCα increases inflammation in asthma and increases the airway remodelling that accompanies the late-stage asthmatic response.14 In the lungs of allergic mice, alpha-tocopherol inhibits, while gamma-tocopherol enhances, the activity of PKCα.
Support for the Northwestern researchers’ theory comes from a study at Vanderbilt University in Nashville, Tennessee, where 33 people with allergic asthma were given 1,500 IU of natural alpha-tocopherol for four months.15 The researchers chose the dietary form of alpha-tocopherol called ‘d-alpha-tocopherol’, derived from a natural source, rather than the synthetic form used in many supplements called ‘dl-alpha-tocopherol’.
This distinction is important because only d-alpha-tocopherol performs the normal functions of vitamin E.
The effect of supplementation was to increase blood levels of alpha-tocopherol and decrease blood levels of gamma-tocopherol. Along with this change in vitamin E, levels of allergic mediators and oxidative stress markers in the lungs also decreased. Airway reactivity to methacholine, a chemical that causes bronchial constriction, also decreased.
The past 40 years have witnessed an increase in gamma-tocopherol in the US diet and in infant formulas, largely due to increased consumption of soybean oil, which is high in gamma-tocopherol.16 (Other vegetable oils, like olive oil, contain minimal amounts of gamma-tocopherol.)
As many vitamin E supplements use soybean oil as a carrier, vitamin E supplements (even if they are labelled as alpha-tocopherol) may act as hidden sources of gamma-tocopherol.
Clinical trials with low-dose vitamin E (usually as alpha-tocopherol) have shown mixed results; the greatest benefits appear to be in people exposed to air pollutants like ozone and sulphur dioxide. Vitamin E in such a setting seems to prevent the increase in airway inflammation produced by air pollution.17
All this research has led me to conclude that vitamin E should not be used as a stand-alone supplement in people with asthma. For one thing, high-dose vitamin E supplementation when used alone can have a pro-oxidant, rather than an antioxidant, effect and so may increase oxidative stress over time.18
It can also reduce blood levels of coenzyme Q10, which is essential for cell function. A European study demonstrated significantly lower CoQ10 levels in the blood of people with asthma.19 When supplements of CoQ10 (120 mg/day) were given to people who needed inhaled steroids to control their asthma, they were able to significantly reduce their steroid doses.20
The bottom line: if you have asthma, choose your vitamin E supplements carefully; opt for natural d-alpha-tocopherol in a soy-free base, and take them as part of a total dietary antioxidant programme and, if needed, include 120 mg/day or more of CoQ10.
The power of fish oils
Besides antioxidants, dietary fat has a significant effect on the risk of asthma, and changing the nature of the fat you consume through food choices or supplementation can have a major impact on asthma control.
Some processed and manufactured fats have a configuration called trans, which lines atoms up on opposite sides of a double bond. Trans fatty acids are produced when polyunsaturated fatty acids are subjected to a process called ‘hydrogenation’, which the food industry uses to prolong shelf life. Natural hydrogenation takes place in the rumen of cattle, so beef and milk contain low levels of trans fatty acids.
The International Study of Asthma and Allergies in Childhood (ISAAC), a global study of half a million children, identified greater trans fatty acid consumption as the most important dietary factor associated with the development of asthma.21
A more modest European study found that consumption of margarine, a major source of trans fatty acids, increased the risk of developing asthma among adults.22
Your body has the ability to make saturated and monounsaturated fatty acids, but it cannot make the major polyunsaturated fatty acids. These are called essential fatty acids (EFAs) and they are divided into two families, called omega-6 and omega-3, based on their chemical structures.
One of the major sources of oxidative stress in asthmatics is the enzyme NADPH oxidase (NOX)—found in mast cells and white blood cells—which causes both inflammation and
Pollen grains have been shown to contain their own version of NOX, so high pollen counts may aggravate asthma even in people who are not allergic to them.
A study from the University of Lecce, in Italy, found that flavonoids in vegetables, fruits, herbs and spices can inhibit excessive NOX activity. Omega-3 fatty acids in fish oils (EPA, or eicosapentaenoic acid, and DHA, or docosahexaenoic acid) have also shown potential for inhibiting excessive NOX activity.23
This may explain why numerous clinical trials have described beneficial effects with omega-3 supplementation in people with asthma.24
Fish oils seem to be especially effective in subduing the allergic reactions in people with asthma. A 20-year study of Americans aged 18 to 30, supported by the National Institutes of Health, found that low dietary intakes of omega-3s from fish more than doubled the risk of developing asthma. The lower the levels of omega-3s consumed, the worse
Such effects were also seen in patients with exercise-induced asthma. When researchers at Indiana University gave 5.2 g/day of omega-3s from fish oil to people whose asthma consistently worsened with physical exertion, they found that fish oil helped to prevent the exercise-induced asthma, while also decreasing bronchial inflammation and reducing the need for bronchodilator medication after just three weeks.26
In a Danish study, pregnant women taking 2.7 g/day of omega-3s from fish oil from gestation week 30 until delivery had children whose incidence of allergic asthma 16 years later was 87 per cent lower than the controls.27
In 1986, I wrote a scholarly article that was published in The Journal of the American College of Nutrition, explaining that people with allergies have an increased need for EFAs because of a block in the way their cells utilize them.28 EFAs can only be got from food and, while both plants and animals can supply you with omega-6s or omega-3s, the EFAs found in animal foods are usually more unsaturated than those in plants.
Omega-3s have attracted so much interest because they have effects in your body that tend to be anti-inflammatory. But the effects of omega-6s, the predominant category of EFAs, are not so straightforward: they may either favour or inhibit inflammation.
Certain omega-6 EFAs may benefit people with asthma, especially when balanced with the appropriate intake of omega-3s. In my experience, balance is the key and more is not necessarily better.
Research conducted by me in the 1980s in association with Dr David Horrobin, an EFA pioneer, and Dr Ross Rocklin, a professor of allergy and immunology at Tufts University, confirmed that people with allergies may have defective omega-6 metabolism, suggesting that some allergic individuals may require special omega-6 supplements to achieve the proper balance.29
In addition, researchers at the University of Wyoming found that some asthmatics actually got worse with high-dose omega-3s.30
As I explained in my review article for the journal Nutrition in Clinical Practice, higher dietary omega-3 levels have been associated with evidence of decreased inflammation in the general population. This has also been observed in people with asthma: higher omega-3 intakes from food result in less inflammation and better asthma control, whereas a high dietary omega-6 to omega-3 ratio leads to poorly controlled asthma.31
The solution might be to combine omega-3s with a unique anti-inflammatory omega-6 fatty acid called ‘gamma-linolenic acid’ (GLA), found in evening primrose oil, black currant seed oil and borage seed oil. Breastfed infants receive GLA in their mothers’ milk. GLA can help overcome the block in omega-6 metabolism that my colleagues and I discovered in allergic individuals during the 1980s.
Other studies also back this up. A combination of GLA (750 mg/day) plus EPA (500 mg/day of this purified omega-3) given for four weeks as a liquid emulsion to allergic asthmatics significantly reduced the synthesis of leukotrienes (proinflammatory agents that make asthma worse) by white blood cells, and also decreased asthma symptoms and the use of bronchodilator inhalers compared with a placebo.32
The tiny bugs inside you
Intestinal microbes may have a profound effect on the development of allergy. Just as the loss of biodiversity weakens a rain forest, a diminished diversity of gut microbes will predispose people to the development of allergy, probably by weakening protective immune responses.33 This raises the possibility that the right probiotics may help people with allergies and with asthma.
Inflammation in any part of the body creates a local environment that favours the growth of microbes that promote further inflammation. This state is called ‘dysbiosis’. From the microbes’ perspective, it makes perfect sense. They thrive on inflammation, so they provoke more of it. It doesn’t really matter if microbes caused the problem to begin with—they soon become the problem.
Having a pet changes the ecology of your home and your body. Families with pets are more likely to share the same microbes, probably because everyone is cuddling the same pet. They’re likely to have a greater diversity of microbes. And having a pet will change the microbes found in house dust.
Researchers at the University of California at San Francisco exposed mice to house dust obtained from a home with a pet dog and a home with no pets. They then attempted to provoke allergic asthma in the mice by sensitizing them to cockroaches and egg whites.
Mice fed dust from the home with a dog were able to resist the development of allergy. When their gut microbes were examined, they had a much greater diversity of bacteria than mice fed the dust from the home with no pets. One particular species of bacteria, Lactobacillus johnsonii, was strikingly present in the allergy-resistant mice. When the scientists fed L. johnsonii to a fresh group of mice, feeding that single probiotic protected the mice against the development of allergic asthma.34
In humans, studies suggest that probiotic supplementation with selected strains of lactobacilli and bifidobacteria may be a helpful adjunct in reducing inflammation and symptoms in people with allergic asthma.
For instance, L. gasseri strain A5, given for eight weeks to children in Taiwan, significantly improved all of the outcomes studied: lung function, asthmatic symptoms and measures of inflammation in blood.35
But the greatest benefits with any kind of supplementation are likely to appear when it’s used as part of a full Allergy Solution programme.
Oxidative stress and asthma
One thing that the lungs of all asthmatics have in common is a condition called ‘oxidative stress’, which increases with the severity of asthma.1
Your body uses oxygen to burn fuel for energy and also to destroy dangerous bacteria. The process, called ‘oxidation’, is like a well-controlled fire, similar in concept to a combustion engine. Your body also has an antioxidant defence system, which controls the fire and keeps it from damaging your own cells.
Oxidative stress results from an imbalance between these two essential activities, oxidation and antioxidation. As all the oxygen in your tissues enters your body through the respiratory system, your lungs are especially prone to oxidative stress, and nothing aggravates that tendency more than inflammation.
Oxidative stress has been proven to directly stimulate bronchial muscle constriction, induce airway hyperirritability and increase mucus secretion.2 It also plays a key role in the well-known link between air pollution and allergic asthma.
Air pollution is an important factor in both the development and worsening of asthma; it can trigger oxidative stress in anyone, but recent research reveals that people with asthma have an exaggerated inflammatory response to air pollution-induced oxidative stress.3
This means it is critically important that people with asthma minimize their exposure to air pollutants, and cigarette smoke in particular.
Cigarette smoke contains more than 4,700 chemical compounds as well as very high concentrations of oxidants (10 trillion molecules per puff). Some of these become trapped in the cells that line the respiratory tract and continue to cause damage for a long time after the smoke exposure ends.4
The Allergy Solution oil change
Follow the principles below to eat the most health-giving fats. If you’re allergic to any of the selections listed below, avoid it and make another choice.
Eat adequate amounts of omega-3 foods. The chief form of omega-3s in plants is alpha-linolenic acid (ALA). Fish contain two other omega-3s—EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)—and your body has the ability to convert some ALA to EPA and DHA. All forms of omega-3s appear to have health benefits.
Good sources of ALA include: seeds like chia, flax, hemp and sabja (or sweet basil); English walnuts (and walnut oil makes a tasty gourmet salad dressing); and green leafy vegetables like spinach and kale (although low in total fats, these can supply ample omega-3s if eaten regularly).
Eat omega-3-rich fish twice a week, unless you’re allergic to fish. Good sources of EPA and DHA include salmon, sardines, trout, mackerel, herring and anchovies. Caution: tuna is high in mercury because it’s a large predatory fish, so don’t eat tuna more than once a month.
Avoid foods made with hydrogenated or partially hydrogenated vegetable oil, as found in margarines and many baked goods. Caution: never trust a label that says ‘zero trans fats’ or ‘trans fat free’, as manufacturers can make that claim if there’s less than 500 mg of trans fats per serving and, by making the serving size small enough, many foods containing these toxic fats can claim to be free of them.
Make extra virgin olive oil your main food oil, and avoid high-omega-6 oils like corn, safflower, sunflower and soybean.
Take omega-3 supplements judiciously. Studies of people with asthma taking fish oils show improvements in measured airflow,1 and significant decreases in symptoms and airway hyper-sensitivity.2 In other studies, improvements were evident within as little as one month with doses of 690 mg/day, 3 g/day and even 5.4 g/day.3
Whey protein: a star is born
Glutathione is the rock star of antioxidants. It’s a team player, supporting the activities of vitamin C, vitamin E and selenium in the body, but it also has an especially important role in helping to maintain the health of your lungs, nose and sinuses. In fact, it is the major antioxidant in the respiratory tract. Many studies suggest that glutathione could be as important for people with nasal allergies and sinus problems as it is for asthmatics.
Levels of glutathione in the nasal lining of people with chronic sinusitis are only half of what’s found in people without sinusitis.1 The greater the degree of inflammation, the lower the level of glutathione.2
Whey supplies the amino-acid cysteine, one of the building blocks your body uses to make glutathione. Availability of cysteine is a well-documented limiting factor for glutathione production.
In a study from McGill University in Montreal, Canada, healthy young adults consuming 30–45 g/day (about two to three level tablespoons) of whey protein significantly raised the glutathione levels of the white blood cells, boosting their ability to fight infections.3
In adults with exercise-induced asthma, 30 g/day of undenatured whey protein taken for four weeks improved post-exercise airflow.4
So, unless you have a cow’s milk allergy (in which case, avoid whey protein), supplementing with whey protein, plus a diet full of antioxidant-rich fruits and veg, may help you control your asthma