Effects of cigarette smoking on semen quality, reproductive hormone levels, metabolic profile, zinc and sperm DNA fragmentation in men: results from a population-based study

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography. Show more

Approximately 37% of men of reproductive age smoke cigarettes, with Europe having the highest tobacco use among all the World Health Organization (WHO) regions. Toxins from tobacco smoking can potentially affect sperm development and function, with a negative effect on semen parameters. Given the high prevalence of smoking and recent changes in the WHO laboratory methods for the examination of human semen, the role of this exposure in face of new WHO methods needs to be clarified. Show more

Tobacco smoking continues to be a major risk factor for cardiovascular disease (CVD) and the leading avoidable cause of death worldwide. Tobacco smoking has declined in high-income countries, but the average smoking rate in Japan remains high: 29.4% for men and 7.2% for women in 2017. Of note, the average smoking rate among middle-aged men remains approximately 40%, indicating that a high incidence of smoking-related CVD will continue for a couple of decades in Japan. The adverse effects of tobacco smoking on CVD are more extensive than previously thought. Physicians should be particularly alert to the development and progression of heart failure, atrial fibrillation, and venous thromboembolism, as well as ischemic CVD among tobacco smokers. Increasing use of heat-not-burn tobacco as cigarette alternatives is an emerging issue. Harmful effects do not disappear just by changing the delivery system of tobacco. Show more