Wellbeing: Natural Highs

We know cycling is good for both body and mind, even if we’re not exactly sure why. It releases endorphins. That’s the best most of us can muster as we regale some poor soul with the time-splits for our latest sportive, or the benefits of hill reps. Heaven forbid we’ll be asked to explain what endorphins actually are.

The term endorphin is derived from two words: ‘endogenous’, a biologist’s term for ‘internal’; and ‘morphine’, the opium-based drug used for pain relief. Endorphins occur naturally in the body and are distributed in the blood and by the central nervous system. Endorphins have, like adrenaline, been providing us with chemical assistance us for as long as humans have needed to fight or fly. Yet we have learned about them only relatively recently.

In 1975, a group of scientists at the University of Aberdeen published an article, in the journal Nature, with the following title: ‘Identification of Two Related Pentapeptides from the Brain with Potent Opiate Agonist Activity.’ Snappy. It documented research, led by two neuroscientists, John Hughes and Hans Kosterlitz, which proved a breakthrough for scientists and sporty types alike.

The brain in question belonged to a pig. From it, Hughes and Kosterlitz isolated a molecule they named ‘enkephalin’ (enkéfalos being Greek for ‘brain’). This enkephalin molecule possessed natural opiates, substances capable of relieving pain in the body, and which we now refer to broadly as endorphins. (The ‘agonist’ of the Nature headline is any chemical that triggers a physiological response.)

These endorphins were miracle molecules indeed. Just as they provide relief when we’re in pain, nor do they waste it if we are not. Indeed, much of the subsequent research on endorphins has centred on the effects they have on athletes. Specifically, the ‘runner’s high’, that feeling of euphoria experienced during periods of exertion. And which seemed to confirm the role played by endorphins in helping the body offset pain when it is under stress. The discovery of endorphins seemed timely; for the jogging boom that swept America in the 1970s and for a Nike marketing department aiming to swoosh all before it.

As the study of neural proteins developed into a scientific field all its own, the phenomenon that had first been observed in runners was applied in a wider context. ‘Endorphin high’ became the new catch-all term, used to describe any exercise, including cycling, which produced a similar response in the body to administering morphine.

More recent research into endorphins, however, suggests they may not hold the whip hand when it comes to wellbeing. In 2003, another study found patients recovering from major surgery displayed, by way of natural pain relief, notably high levels of endorphins in their blood. Equally high levels have been measured by scientists in the blood of healthy subjects during exercise. However, endorphin-related euphoria is generated in the brain, an area that scientists tend not to measure in athletes. To assume any rise in blood endorphins corresponded directly to increased levels in the brain as a result of exercise was precisely that — an assumption.

In 2016, scientists in Germany challenged the endorphin monopoly further. They noted that, while blood-endorphin levels were raised during exercise, it was not possible for those endorphins to pass from the blood to the brain, thus reducing the chances that blood endorphins are responsible for any exercise high. They pointed instead to a previously overlooked source. In 1992, a Czech chemist named Lumír Hanuš discovered a molecule known as ‘anandamide’. One of the first examples of a naturally occurring ‘cannabinoid’ to be identified in the human brain, it also created feelings of euphoria and was thus dubbed the ‘joy molecule’ (‘ananda’ means ‘joy’, in Sanskrit). Crucially, not only do levels of anandamide increase under physical exertion but the molecule is also capable of breaching the blood-brain barrier.

A study in the US that same year suggested the source might be different again. This research noted how mice with low levels of a hormone called leptin ran further than mice whose levels were normal. In humans, leptin works to stop us feeling hungry, essentially keeping us going when our batteries need recharging. Low levels of leptin exaggerate this function, encouraging us to be even more active, ie to seek out food, despite our body’s preference for rest. The function of leptin may well vary between mice and humans, but it may be that leptin creates positive feelings during intense activity.

Elsewhere, scientists have pointed to two long-known hormones, serotonin and norepinephrine. Known as ‘neurotransmitters’, they are produced in greater quantities when you exercise, flooding your nervous system and telling it how great you feel. (Low levels of serotonin and norepinephrine have, conversely, been linked to depression and anxiety.) Serotonin and norepinephrine may also help the body deal with stress simply by forcing it to practise coping with physical challenges. All of which should provide you with sufficient cover the next time you need to justify that weekend ride.