Can smoking cause hormonal imbalances? Just like the negative consequences to heart and lung health, smoking can also negatively impact our reproductive health. Read on to find out.  Quick facts: How smoking affects the body It’s a well-known fact that smoking can have a negative impact on health, with both active and passive smoking being associated with multiple forms of cancer, diabetes and heart disease. Despite this, in the UK, as of 2019, 28% of men and 22% of women aged between 25 and 34 years are current smokers, according to published health data in England (1)—and a whopping 175 million people assigned-female-at-birth (AFAB) smoke worldwide. But whilst smoking’s effects on the heart and lungs are fairly common knowledge, fewer people are aware that it can also influence the body’s hormones. But how exactly are hormones and smoking linked? In this article we’ll look at: Does smoking affect hormones? Despite the lack of public awareness, there is plenty of research that shows how smoking can impact and even wreak havoc on our hormonal health. The chemical components of cigarette and cigar smoke can disrupt the normal functioning of our bodily systems, including the endocrine system. The endocrine system is a network of glands which influence the production, secretion and regulation of hormones throughout the body, such as the hypothalamus, thyroid, adrenal gland, and even the ovaries.  This disruption might lead to lasting effects on all kinds of hormonally regulated processes, including sexual function and reproductive potential, our metabolism and even our sleep.  As mentioned, both active and passive smoking (also known as second-hand smoking) can cause these nasty effects, with some research even indicating that prolonged exposure and inhalation of cigarette smoke can even affect the onset of menopause (3). There are over 4,000 substances in cigarettes that display reproductive toxicity. How does smoking affect different hormones? Smoking has been linked to abnormal changes and fluctuations in various hormone levels, including: Let’s take a look at each of these in detail. Smoking and testosterone Studies have consistently shown that smoking increases testosterone in AFAB individuals. Those who smoke have been found to have higher serum testosterone levels in their blood than those who don’t (4).  This is because smoking is inherently pro-androgenic, meaning it has a positive effect on androgen hormones like testosterone. Increased testosterone levels can bring on side effects such as excess body hair growth (hirsutism), acne, greasy hair and skin, irregular periods and low libido. The main reason for smoking’s pro-androgenic effects lies with nicotine. As tobacco is metabolised, the nicotine within it produces a compound known as cotinine, which inhibits testosterone breakdown (17). However, it’s interesting to note that similar studies performed on ageing men have indicated that, over a long enough timespan, smoking can reduce testosterone levels in those assigned-male-at-birth (AMAB) (16). Smoking and oestrogen As well as being pro-androgenic, smoking is also anti-oestrogenic, which means it has a negative effect on oestrogen levels. Studies have shown that women who smoke have  lower progesterone and oestrogen levels in both their blood and follicular fluid (the fluid which surrounds the developing egg, important for egg growth) (2,5).  Smoking even affects the conversion of androstenedione to oestradiol by cells within the eggs (2). This switch is mainly driven by the effects smoking has on the production of these hormones.  As well as negatively affecting oestrogen production and metabolism by your liver, smoking increases the levels of a hormone called sex hormone-binding globulin (SHBG) which binds to oestrogen—preventing it from performing its essential functions around the body. Symptoms of low oestrogen can include low libido, fatigue, and negative mood changes. Smoking and gonadotropins Follicle-stimulating hormone (FSH) and luteinising hormone (LH) are both gonadotropin hormones. These are hormones released from the hypothalamus (a part of the brain) to regulate the menstrual cycle and induce ovulation.  Unsurprisingly, smoking has been found to affect gonadotropin levels as well. Studies have shown that habitual smokers tend to have higher levels of FSH and LH in the first half of their cycle and during their periods, than non-smokers (6,7).  Disrupted FSH and LH levels can lead to problems with both fertility and menopause. Smoking and Anti-müllerian hormone Anti-müllerian hormone (AMH) is produced by granulosa cells within the ovarian follicles. It’s used as an indicator of ovarian reserve, sometimes referred to as egg count. Research has shown that smokers generally have lower AMH levels. One study in particular found that current smokers have  44% lower AMH levels than non-smokers (8), indicating that smoking can be directly toxic to the eggs within the ovaries. Another study showed that, in smokers, the fluid produced by the granulosa cells (known as follicular fluid) also contains increased levels of harmful nicotine toxins (9). Chemicals derived from cigarettes and smoking have even been detected in the cervical mucus (10). Smoking and thyroid hormones Cigarette smoke has been found to have both inhibitory and stimulatory effects on thyroid hormones. Both active and passive smoking have been linked to decreased levels of thyroid-stimulating hormone (TSH) and increased levels of free thyroxine (T4) and triiodothyronine (T3) (11,12).  Because the thyroid gland plays an important role in the regulation of many different bodily functions such as growth and development, disruption in thyroid level can have huge knock on effects all around the body. The thyroid can also affect fertility.Smoking is consequently a known risk factor for thyroid-related disorders, especially Grave’s disease and Goitres (13,14). Smoking and prolactin Prolactin is produced by the pituitary gland in the brain and is most commonly associated with milk production and altering breast physiology, but it also has a number of different roles throughout the body.  Chronic long-term smoking has been found to be associated with decreased prolactin levels (14), which can cause irregular menstrual cycles, difficulty breastfeeding and negative mood changes. Smoking and cortisol Smoking has also been linked to increased cortisol levels in the blood. It also affects hormones involved in the production of cortisol (2), which can disrupt the regulation of its levels. Cortisol […]