A study published in the ERJ Open Research investigates the relationship between oral contraceptives and asthma attacks. It focuses on two types: combined oral contraceptives (COC) and progestogen-only pills (POP). The researchers aimed to determine whether starting oral contraceptives could impact asthma attack frequency among women of reproductive age.
The study used a population-based cohort from the U.K. Clinical Practice Research Datalink, examining data from 2004 to 2020. This included medical data on approximately 390,000 women aged 18 to 50 with asthma, categorized as either oral contraceptive new users or never users. The new users (two-thirds of the study group) were further divided into COC and POP cohorts.
Researchers used statistical methods to balance out differences among the groups, such as demographic factors, asthma severity, and comorbidities. This way, they could make fair comparisons between those who used contraceptive pills and those who did not.
Key Findings: Contraceptives Study
The study found no significant association between the use of combined oral contraceptives (COCs) and asthma attacks.
However, the use of progestogen-only pills (POPs) was linked to a higher risk of asthma attacks in specific subgroups: women under 35 years, those with eosinophilic asthma, and those who less frequently used corticosteroid inhalers.
For the general population of women with asthma, neither COCs nor POPs had a clear effect on asthma attack rates.
However, what’s notable in this study were the findings on the subgroups. For women with asthma under 35 who were taking the POP pill (also known as the minipill,) the risk of an asthma attack was 39 percent higher than it was for the never users. Those with eosinophilic asthma had a 24 percent increased risk of an asthma attack compared to the never users. As well, women taking fewer asthma treatments, such as daily corticosteroid inhalers, had a 20 per cent increased risk.
Why Minipill May Increase Asthma Risks
The increased risk of asthma attacks with progestogen-only pills likely relates to the way progesterone affects the immune system and airway inflammation.
Progesterone has been shown to increase airway inflammation, particularly in individuals with eosinophilic asthma. This type of asthma is characterized by higher levels of eosinophils (a type of white blood cell involved in allergic reactions), and progesterone may amplify the inflammatory response, increasing the risk of asthma attacks.
Progesterone may also interfere with the anti-inflammatory effects of corticosteroids, which are commonly used to manage asthma. This can make asthma harder to control in patients who are on lower doses of inhaled corticosteroids.
Younger women tend to have higher naturally occurring levels of progesterone. When progesterone from POPs is added, it may increase the hormone levels significantly, exacerbating inflammation in those with asthma.
Unlike combined oral contraceptives (COCs), which contain estrogen, POPs or minipills lack this component. Estrogen has been associated with some protective effects against airway inflammation, so the absence of estrogen in POPs might also play a role.
This combination of factors likely explains why younger women, those with eosinophilic asthma, and those using fewer corticosteroids are at a higher risk of asthma attacks when using POPs.
Study’s Strengths, Weaknesses
The use of a large, nationally representative database strengthens the generalizability of the findings. The researchers tried to reduce biases related to prior contraceptive use. Also, the study carefully considered subgroups based on age, corticosteroid use, and asthma phenotype, providing nuanced insights.
This study did have some limitations. The researchers did not confirm whether participants consistently took their prescribed medications. Relying on health records could lead to inaccuracies, particularly if patients purchased contraceptives without a prescription. In addition, some important variables, such as lung function and physical activity, were not available for all participants.
Real-World Use of Minipill
The findings highlight the importance of considering the type of asthma and patient characteristics when prescribing POPs.
For younger women with eosinophilic asthma or those on lower corticosteroid regimens, healthcare providers should be cautious and closely monitor asthma control when starting a patient on POPs. Further experimental research is needed to clarify the underlying biological mechanisms.
Conclusions
While the study shows no broad link between oral contraceptives and asthma attacks, it points to an increased risk in specific subgroups. Clinicians should take a personalized approach, particularly for younger women or those with eosinophilic asthma.
If you are a younger woman with asthma taking progestogen-only birth control, then I would recommend talking with your doctor about the potential risk of worsening asthma and whether a different type of contraceptive would be right for you.
Continued research into the hormonal influences on asthma management is essential to improve outcomes at a more personalized level.
Dr. Zachary Rubin, a prolific communicator on allergy and medical topics, is double board-certified in allergy/immunology and in pediatrics. Follow his widely read reports on his Substack account and see his videos on Instagram or TikTok.
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