What is FeNO and Why Does It Matter?
Fractional exhaled nitric oxide (FeNO) is a crucial biomarker used to measure inflammation in the airways, specifically eosinophilic inflammation, which is a key feature of allergic asthma. High FeNO levels can indicate active airway inflammation, and the test is used to aid in diagnosis, monitor treatment effectiveness (especially inhaled corticosteroids), and assess a patient's adherence to their medication regimen. Because accurate and consistent measurements are critical for these clinical decisions, external factors that can transiently alter FeNO levels must be considered. This brings us to the complex question of how coffee, a common daily beverage, impacts FeNO.
The Conflicting Research on Coffee and FeNO
The medical literature presents a mixed picture of the relationship between coffee and FeNO measurements, with different studies reaching different conclusions. This inconsistency makes it difficult to draw a single, definitive conclusion without considering the specifics of each study.
Some research suggests that caffeine can significantly decrease FeNO levels, an effect observed shortly after consumption. A randomized, single-blind, crossover study on healthy subjects found that both caffeinated coffee and pure caffeine capsules led to a significant percentage fall in exhaled nitric oxide one hour after ingestion. The mechanism was hypothesized to involve adenosine receptor antagonism. Similarly, a study involving Arabian Qahwa, a traditional coffee-like beverage containing caffeine, also found a significant, though transient, lowering of FeNO levels in healthy volunteers.
In contrast, other studies have found no significant acute effect. A double-blind, crossover study on patients with asthma found no significant change in FeNO levels in patients who drank caffeinated coffee compared to those who drank decaffeinated coffee. This led the authors to conclude that routine abstinence from caffeinated beverages might not be necessary for asthmatic patients undergoing FeNO testing. A third intervention study, this one involving asthmatic children consuming a caffeinated cola, observed a modest and transient rise in FeNO. These contradictory findings highlight the need for careful consideration of study population, methodology, and the confounding factors at play.
Why the Inconsistent Findings?
Several factors likely contribute to the varying results observed in research:
- Subject Population: Differences in study participants (healthy subjects versus asthmatic patients, children versus adults) can influence how FeNO levels respond to caffeine. The inflammatory state of the airways may alter the physiological response.
- Caffeine Source and Dose: The amount of caffeine ingested and its source (pure caffeine, black coffee, cola, traditional preparations like Arabian Qahwa) could play a role. Coffee contains over a thousand bioactive compounds in addition to caffeine, including anti-inflammatory polyphenols and antioxidants, which may counteract or modify caffeine's effects. Additives like sugar and dairy can also introduce confounding variables.
- Underlying Mechanisms: The exact physiological mechanisms linking caffeine to FeNO levels are still being explored. While adenosine antagonism is a theory, other complex interactions involving cyclic AMP or other chemical pathways could be involved and vary between individuals.
- Individual Metabolism: Genetics and individual metabolism can affect how quickly a person processes caffeine, influencing the magnitude and duration of any effect on FeNO.
Practical Recommendations for FeNO Testing
Given the conflicting evidence and the potential for a transient alteration in FeNO levels, the safest and most reliable approach is to follow pre-test guidelines provided by healthcare professionals. Most respiratory health organizations, including Asthma + Lung UK, advise patients to avoid certain items before a FeNO test.
Here are common pre-test instructions:
- Avoid Caffeinated Drinks: Do not consume coffee, tea, cola, or other caffeinated beverages for at least one hour before the test. Some institutions may recommend a longer period.
- Limit Certain Foods: Nitrate-rich foods like beetroot and leafy green vegetables can increase FeNO levels and should be avoided for several hours before the test.
- Abstain from Alcohol: Alcohol consumption can decrease FeNO and should also be avoided for at least an hour prior.
- Refrain from Smoking: Smoking acutely decreases FeNO levels, and patients should avoid smoking or vaping for at least an hour before the test.
- No Strenuous Exercise: Avoid heavy physical activity, which can also affect results.
Comparison of Key FeNO Studies
| Study | Subject Population | Intervention | Observed Effect on FeNO | Time to Effect |
|---|---|---|---|---|
| Bruce et al. (2002) | Healthy adults | Caffeinated coffee / Caffeine capsule | Significant decrease | 1 hour |
| Taylor et al. (2004) | Asthmatic adults | Caffeinated vs. decaffeinated coffee | No significant acute effect | Up to 3 hours |
| Abuzayan et al. (2010) | Healthy adults | Arabian Qahwa (with caffeine) | Significant decrease | Up to 4 hours |
| Afshar et al. (2010) | Asthmatic children | Caffeinated cola drink | Modest and transient rise | 30 minutes |
The Final Word: Adhere to Medical Advice
The complexity of how does coffee affect FeNO is evident in the available research. While a definitive, universally applicable answer remains elusive, the consensus among healthcare professionals is clear: to ensure the accuracy and reliability of FeNO testing, it is prudent to eliminate all potential confounding factors, including coffee and other caffeinated products, before the measurement. This precautionary measure prevents misinterpretation of results, which could have implications for diagnosis, treatment adjustments, and overall patient management. When preparing for a FeNO test, always follow your doctor's specific instructions to ensure the most accurate outcome.
One study showing a significant decrease in FeNO after caffeine intake can be reviewed at the following link: Caffeine decreases exhaled nitric oxide.
