Coffee and caffeine have both positive and negative health effects. Outside of the known effects of increased energy and mental clarity coffee can be a rich source of antioxidants and have numerous studies show health benefits such as protection against cardiovascular disease (1). Coffee is also well known as being a wonderful aid for the liver and helps in preventing a wide array of liver problems and various cancers (2), it is a digestive stimulant and is said to assist in weight loss in both men and women (3) and can be protective against certain degenerative brain diseases like Alzheimer’s, dementia and Parkinson’s disease (4). Caffeine is also widely used to enhance physical performance and exercise, especially for athletes. It is important to remember that despite these impressive benefits, benefits usually occur below 400mg of caffeine a day (about 4 small cups of coffee a day) and this amount generally applies to men. For women emerging research seems to be identifying a lower threshold. Its also important to remember that although some studies have isolated caffeine as having potential health benefits, the vast majority of benefits from coffee seem to also occur from decaffeinated coffee (17).
Caffeine is classed as a drug, it is the most widely used psychoactive drug in the world today (5). It works primarily by stimulating the central nervous system by blocking adenosine receptors leading to feelings of increased energy, arousal and difficulty sleeping (5) Caffeine in turn increases levels of adrenalin and cortisol which can have side effects on the entire body (6). The main reason caffeine is classed as a drug is that it can create dependency, it produces tolerance (meaning more and more caffeine will be needed to produce the desired effect) can have withdrawal symptoms and can lead to intoxication or death if consumed to excess (5). Children, adolescents, pregnant and breastfeeding women are most at risk of negative side effects of caffeine and are advised to avoid or strongly limit caffeine consumption. Caffeine can also interfere with fertility and increase the chances of miscarriage (8).
Although we generally think of caffeine being mostly in coffee, caffeine can be found in a wide array of natural plants including coffee beans, cacao beans (chocolate), kola nuts, guarana, green and black tea, yerba mate, in fact, caffeine is found in various amounts in over 60 different plants. Plants often come well balanced with other constituents that can buffer some of the unwanted side effects of caffeine, however, human processing of the different caffeine-containing plants often serves to increase the caffeine content. Food manufacturers also use synthetic caffeine widely, especially in energy drinks. For the purpose of this article, the majority of the information will be on coffee as coffee is what is most readily used in research studies.
We have known for a little while now that women respond differently to caffeine than men (6) (7). We also know that women can have varying tolerances to caffeine because genetic differences can lead to either slow or fast metabolism of caffeine which can have different effects on the body (14). Despite the difference in caffeine tolerance among women, a study published in 2014 on 350 female university students claimed that habitual caffeine consumption can be linked to nearly all menstrual cycle disturbances including irregular cycles, missing cycles, period pain and heavy menstrual bleeding (13). Here are some of the reasons why:
Cortisol and adrenalin: Caffeine irrefutably raises cortisol and adrenalin in the body. Although it is argued that the body can develop a tolerance over time (meaning it will not raise cortisol as much with longer-term use) the problem arises when women who are already chronically stressed use caffeine to raise stress even further. Increased cortisol and adrenalin in the body can contribute to feelings of anxiety, agitation and insomnia especially as women are more prone to anxiety than men (9). Cortisol and adrenalin cause widespread effects on nearly every other hormone in the body. It affects gonadotropin-releasing hormones (GnRH) (the hormone that initiates the menstrual cycle), prolactin, vasopressin, thyroid hormones and many others. In fact, cortisol can be responsible for the complete shut down of the menstrual cycle and loss of fertility (8). The way each woman’s body responds to stress is highly variable however we know that a woman’s body is more sensitive to the effects of cortisol and adrenalin than males (9) therefore it is important for women to assess if the level of caffeine is too high for their already stressed out system.
Insulin and blood sugar: Generally speaking coffee has been associated with good long term management of glucose and has been found to be protective against type 2 diabetes. Interestingly most of the positive long term effects can be attributed to coffee and not caffeine as some studies have found the same outcomes with decaffeinated coffee (18). Acute short term effects of caffeine show a worsening of the insulin response. Caffeine is shown to spike blood glucose higher than necessary after consumption which leads to a faster drop in blood glucose, this occurs even when there is no added sweetener (13). This is likely due to the increase in adrenalin and cortisol which are directly linked with insulin and blood sugar balance. Glucose impairments throughout the day can leave women feeling like they are on an emotional rollercoaster as well as increase the need for snacking or sugar cravings. Poor blood sugar management is often at the root cause of many hormonal imbalances and is most evident in women that have underlying insulin resistance such as some women with PCOS or women in perimenopause. As blood glucose levels are naturally higher in the luteal phase blood sugar management becomes more crucial in the luteal phase (15). This may be why some studies (but not all) have found some correlation between caffeine consumption and PMS. The caffeine insulin/blood sugar connection is well known in the wellness space and has given rise to things like “bulletproof coffee” and many variations of the idea. The idea is to help curb the negative effects of caffeine on blood sugar while still getting increased energy. The general idea is to drink coffee with or following a meal instead of on an empty stomach as well as add a source of fat like MCT oil or butter (and sometimes protein like raw egg or protein powder) to the coffee to help stabilise the blood sugar response. I have no doubt that this approach would help counteract some of the negative effects of caffeine however the addition of extra calories and saturated fat may have other negative health outcomes for some people. (Personally, I would add nut butter instead of oil as this provides protein and unsaturated fat and is also delicious).
Estrogen: Caffeine has obvious effects on estrogen metabolism in women. 200 mg of caffeine (about 2 cups of coffee) has the ability to either raise or lower estrogen levels depending on genetics and ethnicity (16). Interestingly the source of the caffeine matters as caffeine in soda drinks raised estrogen in all women regardless of genetics while coffee consumption had varying effects (16). Caffeine has a strong direct action on the liver. As estrogen is metabolised in the liver and genetic variations can affect both the metabolism of caffeine and estrogen it is not surprising that caffeine has different effects among women. Both high and low estrogen come with unwanted symptoms, women that have estrogen imbalances may want to consider their caffeine intake and modify it accordingly.
Nutrient deficiencies: Caffeine can both deplete nutrients as well as interfere with the absorption of different nutrients. In particular, caffeine has been shown to interfere with the absorption of iron, magnesium, vitamin D and calcium. Because caffeine is a mild diuretic (it can cause excess loss or depletion of water-soluble nutrients like B vitamins, particularly B1 and B6 and vitamin C (10). All of these nutrients are vital to the normal functioning of female hormones. Magnesium, calcium and B vitamins have important roles in regulating PMS and moods as well as boosting progesterone levels (11). Although there is no clear association between caffeine and PMS (some studies claim no association, some studies claim increased PMS) both the diuretic nature of caffeine which can lead to dehydration and the nutrient depletion caused by caffeine can theoretically make PMS symptoms worse. Iron deficiency anemia is the number one nutrient deficiency in women and is one of the underlying reasons behind heavy menstrual bleeding. This is why many experts recommend taking iron supplementation well away from caffeine so as to not interfere with absorption.
In conclusion, it is obvious that women are more sensitive to caffeine than men. Genetic and lifestyle differences amongst women have a huge impact on how each woman will respond to caffeine. Most experts agree that 400mg of caffeine a day seems to be safe for most adult males, for women there is no agreed-on the amount in the research however based on the current evidence daily caffeine intake seems to be safer at around 200 mg for women and may drop even lower if a woman is attempting pregnancy, is pregnant or breastfeeding or is a child or adolescent. The limit for adolescence is 100mg of caffeine. It is important for all people to monitor caffeine intake especially as some commercial coffee drinks can provide up to 600mg of caffeine in one drink. The source of caffeine also seems to matter. Synthetic caffeine from sodas has consistently been shown to be worse than naturally occurring caffeine in coffee and tea. Similarly, chocolate, although it does contain some caffeine has been shown to have positive effects on women’s hormones (13). Dark chocolate, green tea and matcha have lower amounts of caffeine and have different constituents such as magnesium, theobromine and l-theanine that help curb the effect of caffeine in the body. They are still stimulating but provide a slower more natural release of energy compared to synthetic caffeine or caffeine found in coffee or black tea and are gentler on the central nervous system.
The current research on caffeine and coffee is strongly positive however this does not mean that more is better. It is important to differentiate between the benefits of the whole plant (coffee bean) and isolating the caffeine component. Although caffeine itself does have some medicinal benefits, most of the benefits from coffee can be obtained from decaffeinated coffee, especially when decaffeinated coffee is prepared well using non-chemical extraction eg. the swiss water decaf method of caffeine extraction. For overall hormone health in women, it’s recommended by most health practitioners to keep overall caffeine consumption below 200-300 mg, although more often than not I hear the recommendation to stick to under 100mg, especially in the fertility space. It is also advised to consume caffeine with meals and to switch to gentler forms of caffeine such as dark chocolate, green tea and matcha in moderation. Incorporating caffeine-free coffee alternatives like dandelion tea or chickory is also a nice way to get a similar taste to coffee without the side effects. If coffee is to be consumed it is important to choose good quality organic coffee (either regular or decaf) as coffee crops are some of the most highly sprayed with pesticides and herbicides in the world.
Here are some graphics showing the caffeine content of varying foods and drinks.