What is the estimated annual risk of developing lung cancer for a never-smoker (non-smoker) with an average radon level of 4 picoCuries per liter (pCi/L) at home?

Radon Exposure at 4 pCi/L and Lung Cancer Risk in Never-Smokers

For a never-smoker with average home radon levels of 4 pCi/L, the excess relative risk of lung cancer is approximately 15% per 100 Bq/m³ (roughly 2.7 pCi/L), translating to an estimated 20-25% increased risk at 4 pCi/L compared to minimal radon exposure. 1, 2

Quantified Risk Estimates

The most robust evidence comes from a 2021 systematic review and meta-analysis specifically examining never-smokers, which pooled data from 2,341 never-smoker lung cancer cases and 8,967 never-smoker controls 2:

• Adjusted excess relative risk (aERR) per 100 Bq/m³: 0.15 (95% CI 0.06-0.25) for never-smokers 2
• Converting to pCi/L units: 100 Bq/m³ ≈ 2.7 pCi/L
• At 4 pCi/L (approximately 148 Bq/m³), this translates to roughly 1.22 times baseline risk (22% increase)

A large Swedish study of 436 never-smoking lung cancer cases found similar estimates, reporting 10% excess relative risk per 100 Bq/m³, with relative risks of 1.08,1.18, and 1.44 for radon categories below 50-80-140, and above 140 Bq/m³ respectively 1. Your 4 pCi/L exposure (≈148 Bq/m³) falls into the higher risk category.

Clinical Context and Absolute Risk

While the relative risk increase is meaningful, absolute risk remains important to contextualize 3:

• NCCN guidelines note that residential radon shows a linear relationship with lung cancer risk, though the association is weaker than occupational uranium miner exposures 3
• The EPA action level of 4 pCi/L is based on an estimated 15,000-20,000 annual lung cancer deaths in the U.S. from residential radon 4
• Never-smokers represent approximately 10-15% of all lung cancer cases, with radon being a leading risk factor in this population 5, 2

Important Sex-Based Differences

Men who are never-smokers face significantly higher radon-related lung cancer risk than women 2:

• aERR per 100 Bq/m³ for never-smoking men: 0.46 (95% CI 0.15-0.76)
• aERR per 100 Bq/m³ for never-smoking women: 0.09 (95% CI -0.02-0.20)
• This difference was statistically significant (p=0.027) 2

If you are male, your risk at 4 pCi/L may be approximately 3-fold higher than the average never-smoker estimate.

Critical Mitigation Recommendation

At 4 pCi/L, you are at the EPA action level where mitigation is recommended 4:

• Radon exposures can be prevented through basement sealing or ventilation 4
• Various methods are available for indoor radon reduction when testing shows levels at or above 4 pCi/L 4
• Mitigation is particularly important given that higher indoor radon exposure has been associated with worse survival outcomes even after lung cancer diagnosis 6

Comparison to Other Risk Factors

To contextualize this risk 3, 5:

• Secondhand smoke exposure: RR 1.24 (24% increase) 5
• Occupational carcinogen exposure: mean RR 1.59 (59% increase) 3
• First-degree family history of lung cancer: RR 1.8 (80% increase) 3
• Your radon exposure at 4 pCi/L (20-25% increase) is comparable to secondhand smoke exposure

Methodological Limitations

The evidence has important caveats 7, 8:

• Most individual residential radon studies have limited sample sizes of never-smokers, reducing statistical power 7
• Cumulative radon exposure estimation involves measurement uncertainty across multiple residences 8
• The 2005 meta-analysis cited by NCCN guidelines showed RR 1.14 (95% CI 1.0-1.3) for residential radon overall, with confidence intervals barely excluding no effect 3
• However, the more recent 2021 meta-analysis focused specifically on never-smokers provides stronger evidence with tighter confidence intervals 2