Why do smokers' hemoglobin (Hb) levels increase?

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Last updated: April 16, 2025 • View editorial policy

From the Guidelines

Smokers' hemoglobin levels are elevated due to the formation of carboxyhemoglobin from carbon monoxide in cigarette smoke, which reduces the blood's oxygen-carrying capacity and triggers a compensatory increase in red blood cell production. This process, known as secondary polycythemia, helps smokers maintain adequate oxygen delivery despite the reduced efficiency of their hemoglobin 1. The elevation in hemoglobin levels is typically modest, around 1-2 g/dL above normal, and is reversible with smoking cessation, although it may take several months for levels to normalize after quitting. Key factors contributing to this elevation include:

  • Carbon monoxide binding to hemoglobin, forming carboxyhemoglobin and reducing oxygen-carrying capacity 1
  • Nicotine-induced blood vessel constriction and increased heart rate, stimulating red blood cell production
  • Chronic inflammation from smoking, activating the bone marrow to produce more red blood cells The resulting increase in hemoglobin can increase blood viscosity and contribute to cardiovascular risks already associated with smoking. It's essential to note that COHb levels in smokers can be significantly higher than in nonsmokers, with levels ranging from 3-5% in smokers, compared to less than 3-4% in nonsmokers 1.

From the Research

Hemoglobin Levels in Smokers

  • Smokers often experience elevated hemoglobin levels, which can be attributed to several factors, including carbon monoxide exposure from cigarette smoke 2.
  • Carbon monoxide binds to hemoglobin, forming carboxyhemoglobin, which reduces the amount of oxygen delivered to the body's tissues, leading to an increase in red blood cell production and subsequently, elevated hemoglobin levels 2.
  • A study published in 1978 found that smokers with elevated hematocrits had increased red-cell volume and reduced plasma volume, which can contribute to high hemoglobin levels 2.

Effects of Smoking Cessation on Hemoglobin Levels

  • Smoking cessation can lead to a decrease in hemoglobin levels, as the body's need for increased red blood cell production decreases 3.
  • A study published in 2004 found that smokers who quit smoking using nicotine replacement therapy experienced a decrease in hematocrit and hemoglobin levels, indicating a reduction in red blood cell production 3.
  • Another study published in 2015 found that cigarette smokers develop structurally modified hemoglobin, which can lead to increased oxidative stress and potentially contribute to elevated hemoglobin levels 4.

Nicotine Replacement Therapy and Hemoglobin Levels

  • Nicotine replacement therapy (NRT) can help smokers quit smoking, which can subsequently lead to a decrease in hemoglobin levels 5.
  • A study published in 2012 found that NRT can increase the chances of successful smoking cessation, regardless of the type of NRT used or the intensity of additional support provided 5.
  • However, it is essential to note that NRT may not directly affect hemoglobin levels, but rather, its effects on smoking cessation can lead to a decrease in hemoglobin levels 5.

Comparison of Smoking Cessation Treatments

  • A study published in 2013 compared the effectiveness of varenicline and combination nicotine replacement therapy for smoking cessation and found that varenicline was marginally more effective 6.
  • However, the study did not specifically examine the effects of these treatments on hemoglobin levels, highlighting the need for further research in this area 6.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.