Nicotine, a major toxic component of cigarette smoke, together with carbon monoxide (CO), constitutes a significant environmental exposure with systemic effects. Beyond its addictive potential, chronic nicotine exposure may induce inflammation, oxidative stress, tissue hypoxia, and autonomic imbalance, potentially impairing respiratory muscle strength, functional capacity, and overall physical performance. Additionally, nicotine dependence has been associated with sleep disturbances, cognitive dysfunction, altered pain perception, and reduced quality of life.

Although previous studies have examined individual effects of smoking on specific health outcomes, research addressing these multidimensional impacts within a comprehensive framework remains limited. Therefore, this study aims to investigate the relationship between nicotine dependence level and respiratory muscle strength, functional capacity, cognitive functions, pain, quality of life, physical activity level, and sleep quality, in order to provide a more holistic understanding of the clinical consequences of nicotine dependence.

One of the toxic components found in cigarette smoke, nicotine, together with carbon monoxide (CO), represents an important environmental exposure. Nicotine is the primary component responsible for the addictive potential of tobacco products and rapidly enters the systemic circulation, spreading to both the central and peripheral nervous systems. In addition, the systemic effects of nicotine may influence the oxygenation capacity of respiratory muscles and overall functional performance. Long-term nicotine exposure may trigger inflammatory and oxidative stress responses, which are thought to contribute to reduced respiratory muscle performance.

Sleep disturbances and attention-concentration problems associated with nicotine dependence negatively affect both quality of life and cognitive functions. Studies examining the effects of smoking status on functional capacity have shown that nicotine exposure plays a limiting role in exercise capacity and activities of daily living. One study reported that smokers had significantly lower exercise capacity and physical activity levels in daily life compared to non-smokers. The same study also demonstrated that smoking has a negative impact on the physical components of quality of life and may adversely affect functional independence.

Chronic tobacco exposure contributes to hyperalgesia through multidimensional mechanisms, including dysfunction of central pain modulation pathways, activation of proinflammatory processes, and tissue damage. Research has shown that nicotine dependence sensitizes pain perception, increases pain intensity, and complicates pain management processes. Nicotine has also been found to be directly associated with prolonged sleep latency, reduced total sleep time, and decreased slow-wave sleep, which has restorative properties. Considering that the pathophysiology of common sleep disorders has not yet been fully elucidated, we hypothesize that there may also be a relationship between CO exposure and sleep disturbances.

Chronic nicotine exposure may lead to tissue hypoxia, thereby reducing physical endurance and participation in daily activities. Furthermore, nicotine-induced mitochondrial dysfunction, oxidative stress, and autonomic imbalance may negatively affect general health perception and psychological well-being through symptoms such as fatigue, headache, and cognitive fog. Impaired sleep quality and the presence of cardiorespiratory symptoms may further limit social, occupational, and personal functioning.

Taken together, these effects suggest that nicotine dependence may lead to reductions in quality of life components and cognitive functions. Given the limited number of studies addressing the multifaceted effects of nicotine within a holistic framework, we anticipate that our study-investigating the relationship between nicotine dependence level and respiratory muscle strength, functional capacity, cognitive functions, pain, quality of life, physical activity level, and sleep quality-will contribute significantly to filling existing gaps in the literature.

Inclusion Criteria:

• Regular cigarette use for at least the past 6 months
• No history of respiratory, cardiovascular, or neurological/psychiatric disease
• No recent history of surgery or trauma that could affect respiratory muscles
• No current acute infection (especially upper or lower respiratory tract infections)

Exclusion Criteria:

• Presence of chronic respiratory diseases such as COPD or
• History of cardiovascular disease
• Diagnosed neurological or psychiatric disorders
• history of surgery or trauma affecting the respiratory muscles within the last 3 months
• Pregnancy or suspected pregnancy