Some 432 million adults worldwide suffer from hearing loss, and this number is estimated to double by 2025. About 16% of global cases of hearing loss is caused by exposure to noises that are higher than recommended levels for a workplace. Likewise, nearly 600 million workers are exposed to noises with levels higher than threshold limit value (TLV) (85 dBA) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Noise-induced hearing loss (NIHL) has been introduced as the most important reason for hearing impairment in 7%–21% of workers. Statistics of Bureau of Labor reveal that NIHL is now recognized as the most commonly recorded occupational disease in manufacturing plants that increases hearing loss disabilities in more than 500 million laborers worldwide. They also reported NIHL is among the nine recorded diseases. No statistics have been done on NIHL in Iran; however, this growing health issue is probably more widespread than developed countries.

According to the World Health Organization (WHO), smoking is a serious public health concern. There are more than 1.3 billion smokers worldwide, about 880 million of whom currently live in developing countries. Iran ranks 73rd out of 181 countries in cigarette smoking based on the Tobacco Atlas report. Each Iranian smoker older than 15 consume an average of 936 cigarettes per year. Iran is among the list of countries that have not addressed smoking well. According to WHO, about 20.2% of Iranian men over the age of 15 smoke on a regular basis, and this recently has been increasing. Smoking has several hazards to the health—-increased risk of cancer, premature death, respiratory tract infections, and increased amount of pollutant in the environment.

However, results from three out of eight cohort studies showed a relationship between smoking and hearing loss,  whereas others did not find any effect of smoking on hearing loss. Because noise exposure might be a significant factor that interacts with (or affects) the effect of smoking on hearing loss, our study aimed to assess the impact of smoking on hearing loss among workers exposed to industrial noise 85 dBA or higher at a metalwork plant in Arak, Iran.

Article originally appeared on The Hearing Journal