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Sex and Sleep hormones

"To control your hormones is to control your life" - Barry Sears

Thank you for joining me for blog 28 highlighting decision-making and the brain. This is my public exploration of what drives decision-making and how we can use that information to make better decisions, resulting in better outcomes.

Today's blog ends the series about certain hormones by focusing on adrenaline, sex hormones and sleep hormones. Excitingly (for me anyway), next week there will be a zooming out, and answering generally, 'what do some key hormones do to our decision-making'.

A huge caveat, is that as with all the other hormones there are many things going on behind the scenes. I have for ease of narrative kept it simple and tried to capture the main effects.


When we were kids and felt slightly scared but exhilarated by the big slide, we got an adrenaline rush. Adrenaline is much like cortisol in that it is released in response to perceived danger, and it has the impact of increasing focus. That focus enhances the experience with the added bonus of dulling pain. Common activities that release adrenaline are those which we associate with thrill-seeking e.g. watching a horror movie, skydiving, cliff jumping, bungee jumping, cage diving with sharks, zip lining.

Similarly to cortisol, decision-making with high amounts of adrenaline in your system will be likely to be rushed and knee-jerk. Additionally, people who see life as dull or unexciting might intentionally take risks that generate adrenaline, which might include stealing or driving too fast. This 'spicing up' will lead to situations that make no sense if viewed from a totally rational lens e.g. why did a wealthy actress steal something she could easily afford?

Sex hormones - Testosterone

Testosterone, as you would expect is mostly related to reproduction both in terms of physically and behaviorally. It is present and important for both women and men, but men tend to have 10-20x the amount and therefore more important in understanding male behaviour. The key insight is that testosterone in men, leads to more motivated, competitive and aggressive behavior. Evolutionary biologists think that this risk-taking is more likely to result in social dominance and social dominance increases the chance that a male finds a mate.

Men in committed relationships on average had lower testosterone levels than those who were either single or who conducted extra-marital affairs. Fatherhood also decreased testosterone levels - perhaps these adaptations have increased the survival probabilities of offspring.

Unsurprisingly, risk-taking of all stripes was correlated with higher testosterone. In young adult males, a clear example was in a financial risk-taking, where those with higher testosterone were more likely to take financial risk according to a Harvard study. The way someone might view a risk might be more to do with their testosterone levels that day than a reliable picture of how they might view that risk over time.

Unusually low testosterone is associated with a lack of confidence, motivation and poor concentration.

Sex hormones - Estrogen

Estrogen is present in both men and women although this time the skew is that women have 10x more estrogen and therefore it aligns more closely with female behaviour.

Estrogen is highest during a female's high fertility years and seems to have many mood, memory and focus benefits that testosterone has in men. It is easier to understand estrogen's impacts when it is withdrawn. Low estrogen e.g. menopause is understood to cause low moods, obsessive compulsive behaviour and binge eating. Therefore Estrogen appears to offer elements of confidence, focus and self-control and therefore decisions might be impacted by Estrogen levels.

Sleep hormones - melatonin and adenosine

It seems, that for good mental and physical health and a league of other benefits, sleep is a key input. It is largely controlled by two hormones: adenosine and melatonin. They work together to reinforce our circadian rhythms. Circadian rhythms are daily patterns we follow which regulate our behaviour and is very important for sleep. We sleep better if we have regular bed and wake up times.

Melatonin is a hormone that makes you feel drowsy at higher concentrations. It is generally produced on the onset of darkness and light causes our melatonin production to stop. Insomnia or poor sleep quality might be brought about by too much light exposure (especially blue light) which reduces the production of melatonin. Large variance in bed times for example, jet lag can disrupt the natural pattern of melatonin and we sleep best when we work with our natural circadian rhythms. Some people take melatonin pills to help them combat insomnia.

Adenosine, the other key hormone also drives sleep when in high quantities. It is a by-product of burning energy in your body so unsurprisingly highly energetic days leads to more sleep drive. I find that days where I move very little, I find myself less tired and more restless. Doctors recommend exercise during the day (preferably a long time before bedtime) for good and deep sleep.

Poor sleep impacts decision-making by making you cognitively impaired. You are more likely to make unsound conclusions and be less able to process complex information.

So what?

How is this all relevant to decision-making? Here are three take-aways I want to leave you with before we pick it up next week:

1) Adrenaline is the excitement that accompanies daring deeds, but seeking it out might lead to decisions that in hindsight look poorly thought through

2) Sex hormones (testosterone and estrogen) have a big impact on focus, confidence, risk-taking and self-control

3) Sleep is a key ingredient to good decision-making and is helped through the production of melatonin which is brought on by darkness and adenosine which accumulates through activity.

Thank you for joining. Next week we will do a summary blog 'Rational people don't have hormones'.


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