Is Coffee Dehydrating and Bad for Your Hormones?
I LOVE coffee, and it’s not just because I’m addicted to caffeine, I switched to decaf a few years ago. I truly love the taste for some reason tea has never been able to replace my morning coffee ritual. But I do think that things like Bulletproof coffee has unnecessarily elevated it to superfood status.
Like any food, medication, or supplement coffee has a list of things that are good about it and things that are not so good about it. One of the biggest negative things I hear about coffee is that coffee is dehydrating, which is actually not true. But on the flip side, coffee doesn’t actually wake you up and make you feel more energized, it activates your stress hormones and gives you a false sense of wakefulness.
Do I drink coffee every day? Can coffee play a role in improved athletic performance? Yes. Is coffee a superfood that should be consumed without abandon? Not really.
The health benefits of coffee are related to its high polyphenol content. Polyphenols are substances from plants that help to prevent inflammation and oxidative damage in the body. Polyphenols also benefit gut health by promoting the growth of “good” bacteria in the gut.
Does coffee cause dehydration?
I found several studies that indicated that moderate (or “casual”) coffee consumption does not affect fluid balance and even potentially provides the same amount of hydration as water. , , 
Another study (I only found it summarized, I was unable to find the actual study) looked at 75 years of data and determined that moderate to high caffeine consumption (240-642mg) does not have any more of a diuretic effect than plain water and it does not contribute to dehydration, negative exercise performance, nor does it impact temperature regulation in a hot environment. They did note that moderate caffeine consumption might slightly increase sodium loss, but given the average amount of sodium consumed this isn’t a huge issue. This study also claims that even though caffeine is a diuretic, the overall fluid balance remains the same because the body retains the fluid from the beverage (different than taking a pill that has a diuretic effect) and that people regularly consume caffeine adapt to the diuretic effects and lose even less water.
In the context of athletic performance, the effects on hydration and sodium loss appear to be negligible. Caffeine intake around physical activity does not increase body temperature, oxygen consumption, or fluid balance.  While coffee might not be the best option for a sports drink, caffeinated beverages do not appear to negatively impact your fluid balance (i.e. hydration status) during physical activity.
There are some downsides to caffeine for some people. There are a whole host of genetic factors that affect how you tolerate caffeine and you caffeine tolerance generally decreases with age. Slow metabolizers of caffeine should be careful with caffeine consumption.
Does coffee actually wake you up?
So many of us don’t feel like we can start our day without coffee. So how does your morning cup of coffee actually turn you into a contributing member of society, is it REALLY giving you an energy boost?
The short answer is no, it doesn’t. What it really does is make you feel like you have energy by blocking the ability of your body to feel tired. This is why it’s such a powerful substance in the context of athletic performance.
Caffeine resembles a substance we have in our bodies called adenosine. Adenosine slowly builds up in our systems throughout the day to eventually make us feel tired and go to sleep. Caffeine has the ability to bind to the adenosine receptors, but does not have the same sleepiness inducing effect.  This means that caffeine is actually making us feel less sleepy and not giving us more energy.
Because over-expression of the adenosine receptor is seen in people who experience chronic stress (yes, too much exercise is chronic stress) and people with HPA axis dysregulation, it’s possible that this upregulation of the adenosine receptors might be a response to chronic stress.
Unfortunately, many people ignore this signal of high adenosine activity which is telling us to slow down. Instead we caffeinate and carry on, repeating the cycle the next day. Because coffee doesn’t actually energize you, it just masks the signals from your body telling you that you’re tired, it’s more of a bandaid than a solution for actual low energy levels.
coffee and your stress hormones
Any athlete is susceptive to HPA axis dysregulation (also called adrenal fatigue), but especially those of us who are endurance athletes. HPA axis dysfunction is typically the root cause of chronic fatigue, but it’s very clear that chronic fatigue is NOT a coffee deficiency.
Coffee tends to mask HPA axis dysregulation AND has the potential to make it worse.
Doses of caffeine as low as 2mg/kg have been shown to activate the HPA axis.  Continual activation of the HPA axis, whether from chronic stress or caffeine, is what leads to eventual chronic fatigue and HPA axis dysregulation.
If you are an athlete it’s especially important that you pay attention to the way you are using caffeine as well as your overall training load and stress levels. You can still train hard and feel good, but rest becomes a very important part of the process as well as listening to what your body is telling you. If you’re having to push through excess fatigue too many days, you may not be getting proper rest/recovery and you should be aware of potential HPA axis dysregulation.
coffee and your thyroid
Your thyroid hormones and your HPA axis are intimately related. Coffee has the potential to suppress the function of your thyroid due to an increase in cortisol levels. Increased cortisol levels can down regulate your thyroid hormones.
HPA activation, through the stress response, causes a release of cytokines which have been shown to lower thyroid stimulating hormone (TSH).  TSH is what tells your thyroid to make more hormones (it’s released from the pituitary gland in your brain). Lower TSH will result in lower thyroid hormone production.
Increased cortisol prevents the conversion of the inactive form of thyroid hormone (T4) into the active form of thyroid hormone (T3).  This can lead to symptoms of hypothyroidism such as weight gain, depression, fatigue, and hair loss.
If you feel you are sensitive to caffeine and you have a thyroid issue, consider switching to decaf or taking a break from regular coffee drinking. It’s also important to note that drinking coffee within an hour of taking thyroid medication can decrease the absorption of your medication.
Coffee and Athletic Performance
There is evidence that shows that caffeine enhances endurance and improves performance in a variety of different types of physical activity such as high-intensity events, prolonged high-intensity events, endurance events, ultra endurance events, and prolonged intermittent sprint events such as team sports. 
Caffeine might also increase the contractile force of skeletal muscle and increase an athlete’s threshold for pain and perceived exertion.  Because of it’s powerful antioxidant effects, caffeine, especially from coffee, can help to combat the muscle damage that is caused by exercise. 
As far as physical performance is concerned, the evidence is varied in terms of effective dosages of caffeine. This is likely due to the differences in individual caffeine metabolism. The optimal dose of caffeine appears to be the one where you do not experience any of the negative effects such as increased blood pressure, headache, or high heart rate, but still benefit from the ergogenic effects of caffeine. High doses (up to 6mg/kg) do not seem to increase the benefits to athletic performance and appear to have a higher incidence of side effects.
The Bottom Line
The take home message in all of this is that coffee is not a superfood and it should be consumed in moderation, especially if you are sensitive to the effects of caffeine.
Moderate caffeine consumption will not cause dehydration, in fact it will probably help you with your athletic performance. However, it may have a negative impact on your hormones (but that also depends on a lot of factors).
If you don’t already use caffeine, don’t start. Most caffeine containing beverages are not good for you (soda, energy drinks, coffee drinks) because they contain a lot of sugar. Caffeine will not make you a better athlete, it only helps to improve already well trained systems. Caffeine is definitely not a substitute for good old fashioned training.
Large amounts of caffeine can have a negative impact on your health. It can raise blood pressure, especially during times of psychological stress, and it can cause increased heart rate and even arrhythmias in certain susceptible people. It’s also important to remember that the effects of caffeine change as you age because your caffeine metabolism slows down, so if you once could drink unlimited coffee and feel no negative effects, it’s possible that after several years you feel negative effects after 2 or 3 cups.
And even though the evidence shows that coffee does not cause dehydration, please use you common sense and drink plenty of water…using coffee as your main form of hydration is definitely NOT a good idea!
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