Twenty surprising things your hormones make you do - without you realising it. From making you cheat to making the men in the office treat you better

They are linked to everything from Parkinson’s to weight gain, anxiety and an excessive libido. And yet, so much of how they operate within our body remains mysterious.

I’m talking, of course, about hormones. Produced not only in the brain, but also in our gut and even our body fat, these infinitesimal chemical substances do nothing short of making us who we are. Put simply: we are our hormones.

For while our brain is central to all the decisions we make, the 50-or-so hormones in our body — and more may be discovered — in turn influence how our brain functions.

I’ve been a specialist in endocrinology (the study of hormones) for almost 20 years. And almost my entire family suffers from some sort of endocrine disorder — from diabetes to thyroid disorders and even adrenal gland tumours (a non-cancerous growth) — so I see proof every day of how a hormonal imbalance can play havoc with both our personality and day-to-day health.

I recall, for example, a female patient who became sexually disinhibited due to an overactive thyroid — a butterfly-shaped gland in the neck that produces hormones that affect nearly every part of your body, including sex hormone levels — and ended up in bed with a male patient in our clinic. Only when her thyroid was surgically removed did she return to her old self.

Hormones have played a surprisingly significant role in world events. For instance, President John F. Kennedy had the rare autoimmune condition Addison’s disease, which meant his adrenal glands produced less cortisol and aldosterone (which helps control the balance of water and salts in the kidneys, among other things). Your skin can also turn darker, like a tan.

Our body produces 50 or so hormones (and more may be discovered) which influence how our brain functions

Back then, JFK received cortisol and testosterone injections to combat all this — but one missed injection during protracted negotiations with the Soviets over the Cuban Missile Crisis left him as limp as a wet rag and, say historians, severely raised diplomatic tensions.

As for whether those testosterone injections influenced his womanising... well, it’s not inconceivable.

It’s even possible to see the role of hormones in the English royal line of succession. Queen Mary I — daughter of Henry VIII, and also known as Bloody Mary — continually believed herself pregnant; her stomach swelled, she produced milk, but unfortunately no child was ever delivered. Later, she became essentially blind.

It’s likely this was due to a tumour of the pituitary gland (a pea-shaped gland at the base of the brain). It makes hormones that regulate other hormone glands and are responsible for the body’s growth, metabolism and fertility.

It was in part due to Mary’s childlessness that the House of Tudor died out and that, after the Stuarts and the Hanoverians, the House of Windsor came to the throne.

Tiny though they might be, clearly hormones are powerful for all of us. Here — from choosing partners, to your behaviour at work, to arthritis — are 20 fascinating facts about how hormones affect our bodies…

A DIP IN IMMUNITY — AND AN UNEXPECTED BLESSING

None of us would exist without progesterone. Produced by the ovaries, it’s vital to help a fertilised egg implant in a mother’s womb.

And in the final part of pregnancy, progesterone protects the baby again, by temporarily turning down the mother’s immune system so it doesn’t see the baby (half of which, after all, consists of ‘foreign’ DNA) as a dangerous intruder. The flip side being that pregnant women are often more susceptible to infections which may be more severe, as we saw with Covid-19.

But this lower immunity can be beneficial for women with autoimmune conditions — where your immune system attacks your own body, such as rheumatoid arthritis or thyroid disease. These often become less severe in pregnancy, thanks to progesterone.

It’s striking that autoimmune conditions are nearly nine times more common in women than men. And a major reason for this may be that oestrogens stimulate some immune cells that attack endocrine glands such as the thyroid. However, testosterone — a predominantly male hormone — has a curbing effect on autoimmunity.

After the menopause, women are less likely to develop autoimmune conditions as they have lower oestrogen levels, leading their immune system to behave more like that of a man.

Pizza, which affects our endorphins - or 'happy hormones' - tops the list of most addictive foods in a study published in the US National Library of Medicine

WHY YOU CAN’T SAY NO TO CHEESE-LADEN PIZZA

Pizza topped the list of most addictive foods in a study published in the U.S. National Library of Medicine — and its success could be down to its effect on hormones called endorphins, or ‘happy hormones’.

These morphine-like molecules, that are also referred to as our natural painkillers, largely originate in the brain. Childbirth and endurance sports stimulate their release in order to help the body deal with pain — as do some foods.

Biologists suspect cow’s milk, as well as providing calves with nutrition, also has something of an addictive effect on the calves, as it provokes a release of endorphins, helping to keep them close to their mothers.

Extraordinarily, this compulsion also might be passed on through the food chain. Cheese made from cow’s milk contains a lot of casein — an animal protein which gives anyone eating it a rush of endorphins comparable to that which calves receive from nursing at their mother’s udders. This may explain why people who have long outgrown the nursing stage get the same ‘fix’ from cheesy pizza.

CLUES THAT MUM-TO-BE IS CARRYING A BOY

Forgetfulness, a big appetite and strange food cravings are more commonly seen in women who are pregnant with boys. Why?

Blame the hormones! Influenced by the higher testosterone levels coming from the growing male foetus, these women are more likely to see off a whole bag of sweets or to crave gherkins than those pregnant with a girl.

This could explain why boys generally have a higher birth weight than girls; they have simply received more nutrients.

ANOTHER REASON TO BREASTFEED, IF YOU CAN

Breastfeeding can make for a more peaceful perimenopause — the time when a woman’s ovaries gradually stop working. One study found women who breastfeed for longer are proven to have lower and more stable oestrogen levels during their perimenopause, although it is still unknown why.

THE REASON YOU CAN’T KEEP THE WEIGHT OFF

We know the maths: if you consume more calories than you use, you gain weight. And once we put on the pounds, our body seems to do all it can to maintain an increased weight. It’s as if we have a built-in thermostat to keep it at what the body thinks is the ‘right’ level, or set-point weight.

Your set-point weight is maintained by the hormone ghrelin, the ‘hunger’ hormone driving our appetite. Levels of it are higher in the blood of obese people, although it’s not clear if this is a cause or an effect.

The problem is that those who eat more over a long period of time not only achieve a higher body weight, but also a higher set-point weight, making it harder to return to a slimmer size.

This explains the yo-yo effect we often see when people diet, whereby someone who has lost a lot of weight quickly puts it all — or sometimes even more — back on.

...ESPECIALLY IF YOU ARE OVER 50

Anyone aged over 50 who’d love to lose that last half a stone will be au fait with calorie-counting and carb restriction. But it’s not quite so likely they’ll know about the ‘satiety hormone’ leptin.

Produced by your fat tissue, leptin signals to the brain that you’ve eaten enough. Its system is wonderfully balanced. If your energy reserves are too low, your fat percentage decreases, and along with it your leptin level, which then increases your desire to eat — and vice versa: if your leptin level is high, you’ll be more easily satisfied by your food.

However, the ageing body can become resistant to leptin. This shows how vital it is to sustain our muscle mass and fitness as we age to counteract the natural changes in hormones that can make losing weight difficult.

If your teen is going to bed very late due to scrolling on social media, the quality of their sleep will be poor - and can stunt their growth

LATE NIGHTS ‘SHRINK’ YOUR TEEN

Struggling to get your teen off their iPad or phone before bed? Try telling them it could make them shorter.

This is because nighttime is rush hour for the body’s hormonal traffic — including growth hormone. This is mostly delivered to the body from the pituitary gland at the base of your brain, during the deep, slow-wave sleep of the first few hours of the night.

So if your teen is going to bed very late due to scrolling on social media, the quality of their sleep will be poor. And even if they sleep in, as they’ve missed those vital hours before midnight their production of growth hormone will be affected.

Ultra-processed foods create bad gut bacteria, lowering the levels of serotonin and dopamine created by the small intestine

PLEASURE HORMONES IN YOUR GUT!

We think of hormones as being a creation of the brain or glands, but your gut is vital for hormones, too. More than 90 per cent of all serotonin — the happy hormone targeted by many anti-depressants — is made in the small intestine and is potentially controlled by the bacteria that live there.

Similarly, 50 per cent of dopamine — the pleasure hormone — is made in the gut.

Western diets full of sugar and ultra-processed foods, which cause an increase in bad gut bacteria, are then hugely significant to hormonal health. Indeed, Cambridge professor of psychiatry Edward Bullmore explained in his 2018 book The Inflamed Mind how a digestive system with bad gut bacteria can lead to illnesses like depression (through lack of serotonin), Parkinson’s disease (through lack of dopamine) and dementia (through chronic inflammation of certain brain cells).

WHY YOUR MEMORY IMPROVES ON THE PILL

There’s been a recent backlash against the Pill from a generation of women seeking a more ‘natural’ lifestyle. It does appear that there’s something in their complaints about the Pill making you feel different.

First, that it reduces libido. This is probably because a lengthy period of hormonal ‘supplementation’ — which is what the Pill does, by inhibiting ovulation through releasing oestrogen and progesterone — has the knock-on effect of suppressing the production of a woman’s own sex hormones.

The result is consistently high levels of progesterone and oestrogen, but fewer androgens, such as testosterone (women do make testosterone, but in much smaller quantities than men). These lower testosterone levels also cause prolonged fatigue.

But there is one unexpected and beneficial side-effect: research shows the Pill can improve your memory.

In an experiment, women who did and didn’t take the Pill were shown films, then a week later asked what they could remember.

The women with a natural cycle remembered the emotional parts much better, whereas those who were on the Pill were able to summarise the story better, as men usually do. From this, we can deduce that a natural hormonal balance helps you remember emotional details, but the Pill focuses your attention more on the core of the matter.

TOO MUCH TESTOSTERONE CAN MAKE MEN GIRLY

Bodybuilders tempted to bulk up, beware: hormonal supplementation through steroids can actually make you girlier. This is because your own body tries to convert all that excess testosterone via body fat into female hormones, namely oestrogens.

This can lead to infertility and the development of mammary glands in men. The hormone injections also inhibit production of the body’s own testosterone, causing the testicles to become smaller, sometimes permanently.

There’s evidence that yoga should be treated like hormone therapy as it reduces chronic stress and inflammation

YOGA IS LIKE HORMONE THERAPY FOR WOMEN

Yoga is known for making you more flexible — but there’s evidence we should think of it as hormone therapy, too, reducing chronic stress and inflammation.

Blood sugar levels and cortisol, the stress hormone, also tend to be reduced in those who practise yoga.

These are associated with polycystic ovary syndrome, which is a common cause of infertility in (often overweight) women who have ovulation problems.

Yoga can stimulate the production of sex hormones in these women, making them menstruate more regularly and so could improve fertility.

COULD CUDDLE HORMONE TREAT AUTISM?

Produced by the hypothalamus, the area of the brain which controls both nervous and endocrine systems, oxytocin (dubbed the ‘cuddle hormone’) is released whenever you’re in contact with loved ones.

Socially neglected children with a shortage of oxytocin display behaviours similar to autism. Researchers also found that when oxytocin is administered to people with autism via a nasal spray, it made them more sociable.

As men age, studies suggest that they care less for hierarchy and become more personable due to their lower testosterone levels

MEN BECOME NICER AT WORK AS THEY AGE

Working in HR? Perhaps you should be aware of how age-related hormonal changes can affect employees’ workplace behaviour. Studies found that as they age, male employees care less for hierarchy and become more personable — thanks, presumably, to the dip in testosterone.

VOCAL CHANGES AROUND YOUR PERIOD

A husband may spot the signs of his wife’s approaching period in her deteriorating mood — but there’s an intriguing way to spot that she may be ovulating, too. Studies have found that in menstruating women, their voices are higher around ovulation, thanks to the surge in hormones.

Indeed, so pronounced is this effect that some singers schedule their work according to their menstrual cycle or take hormonal contraceptives to protect the quality of their voice.

MEN’S VOICES GET HIGHER AS THEY AGE

Both sexes experience voice changes as their hormone levels change with age: men’s voices usually get higher because their testosterone levels fall, whereas women’s voices deepen as their oestrogen levels reduce. For female professional singers, this ‘post-menopausal voice syndrome’ can be problematic for their careers.

As for men, the higher pitch of their voice may signal their fertility is coming to an end. Scientific research confirms women are more attracted to men with deeper voices — especially when women are at their most fertile.

AND BAD NEWS FOR MEN’S BLADDERS, TOO

While men aren’t troubled in the same way as women by urinary tract infections in their youth, bladder infections become more common for chaps as they age — owing to hormones.

As men get older, their prostate grows in response to the presence of a hormone called dihydrotestosterone. This potentially impedes their urethra and can mean men are less likely to be able to empty their bladder — and so the risk of infection increases.

WOMEN’S FACES CAN BECOME SQUARE-SHAPED

Some older women say one day they looked in the mirror and suddenly no longer recognised the face looking back. This could be down to their hormones.

As a woman ages and testosterone becomes more dominant, their face shape appears to change: in particular, this affects the ratio between the length and width of the face.

The higher the testosterone level, the wider the face becomes related to the length. For boys in puberty, this leads to the formation of an adult face.

n Adapted from The Power of Hormones, by Max Nieuwdorp, to be published by Simon & Schuster at £25, on May 23. To order a copy for £22.50 (offer valid to May 21, 2024; UK P&P free on orders over £25), go to mailshop.co.uk/books or call 020 3176 2937.

Why some men can’t stop themselves being unfaithful 

FATHERHOOD DIALS DOWN A MAN’S LIBIDO

Fascinatingly in the last trimester of the mother’s pregnancy, a father’s testosterone levels fall, before an extra dip after the birth.

This is part of a biological adaptation to ensure the dad will help care for his child. Testosterone can exacerbate physical aggression and increase libido — traits hardly ideal for new fathers.

Indeed, research shows men without young babies have less oxytocin — the ‘cuddle hormone’ — and more testosterone in their blood. Their brains are also quicker to react to sexual stimuli.

Becoming a dad often lowers libido - but can in fact drive some men to eventually cheat on their partner

...BUT SOME ARE DRIVEN TO CHEAT

However, not every new father is hormonally driven to fixate on the family. Men may also have a tendency for infidelity after having children, potentially because cheating causes the pleasure hormone dopamine to be released.

Kissing can be a way to test for fertility levels as saliva produced while ovulating is sweeter, containing more sugar

It’s interesting also to note that the stress hormone cortisol plays a role in seduction, with a different effect in men and women.

If you’re a woman with a high level of cortisol, you’re less receptive to seduction attempts, whereas stressed men are more open to these — perhaps through the prospect of lovemaking as a quick way to relieve stress.

HOW TO TELL WHEN YOU’RE MOST FERTILE

It’s all in your kiss. Researchers have found that, due to the influence of oestrogen, women can send messages about their fertility via their saliva. Around the time of ovulation, for example, saliva contains more sugar, so a woman’s kisses literally taste sweeter at this time.