Most of us have a routine for waking up in the morning.
We get up, check our mobile phones, get out of bed and, for a lot of us, drink a cup of coffee.
But before coffee, breakfast, vitamins or supplements, there is a more basic thing that we have to consider – water.
During the sleeping hours, your body doesn’t stop working: you keep breathing, your heart keeps pumping, your kidneys keep controlling fluids and electrolytes, and water makes its way out of your system through respiration and the skin.
The estimated water loss overnight is approximately 300-500mL per eight hours through respiratory and skin pathways.
This is why water should be the first drink in the morning as you have spent several hours not taking any fluid while continuing to lose it.
Water leaves the body overnight, leading to a decrease in plasma volume, and blood cells may become more concentrated in a process known as hemoconcentration.
After an overnight fast, blood can be slightly more viscous, but this does not pose a danger of dehydration or “thick blood” for most people.
The body effectively regulates circulation and fluid balance.
However, it’s wise for older adults and those who don’t drink enough during the day to rehydrate after sleeping, considering the cardiovascular system’s function in the morning.
Rapid physiological change
Waking is not just the moment when your eyes open.
Your body goes through a coordinated transition from sleep to activity.
Cortisol usually rises around waking; sympathetic nervous system activity changes; heart rate and blood pressure start to adjust to a calm, upright, active state; and platelet activity and vascular function follow circadian rhythms.
Some studies show a morning pattern of cardiovascular events but it would be an oversimplification to say that overnight dehydration causes morning heart attacks or strokes.
There are four potential factors that are related to waking: the cortisol awakening response, sympathetic activity, platelet aggregability and increased blood viscosity.
That makes morning hydration an appealingly simple intervention.
But it should be viewed as part of good hydration practice – not a method of preventing a heart attack.
Interest in cold water
Cool or cold water may have further effects through temperature-sensitive receptors in the digestive system.
One receptor receiving particular attention is Transient Receptor Potential Melastatin 8 (TRPM8).
TRPM8 is a temperature-sensitive ion channel involved in detecting cooling and can be activated chemically by menthol.
The material describes TRPM8 receptors associated with the gastrointestinal sensory system and proposes that cooling can generate signals transmitted through vagal pathways.
This brings us to one of the body’s most remarkable nerves.
Meet the vagus nerve
The vagus nerve – cranial nerve X – is a major communication pathway connecting the brainstem with the heart, lungs and digestive tract.
It plays a major role in the parasympathetic nervous system i.e. the body’s “rest and digest” system.
The vagus is intimately linked with the oesophagus as it travels through the chest, and vagal pathways play a significant role in swallowing, gastric function, intestinal activity and cardiovascular physiology.
It is therefore biologically plausible that temperature and mechanical stimuli in the gastrointestinal tract can generate sensory signals that ultimately influence autonomic activity.
What is much less certain is the claim that drinking water at a precise temperature, such as 10-15°C, can reliably turn the whole body into a parasympathetic state for several hours.
That is a very interesting hypothesis, but current physiology should not be extended to clinical certainty.
Two different signals
When you drink a glass of water, your stomach receives more than a chemical substance, it receives volume.
Stretch-sensitive receptors detect gastric distension.
These signals are involved in digestive reflexes such as the gastrocolic reflex, in which filling the stomach can trigger movement in the colon.
This is why some people feel the urge to empty their bowels after breakfast or a morning drink.
Cold water could also provide another signal: temperature.
Mechanical stretch and thermal stimulation may converge through vagal pathways and may influence gastrointestinal motility.
The gastrocolic reflex itself is well-known.
The claim that cold water produces a significantly stronger reflex than room-temperature water, however, requires better clinical evidence before it can be recommended as a treatment for constipation.
If cold water agrees with you, stick with it.
If room-temperature water feels better, there is no compelling reason to force yourself to drink cold water.
What about coffee?
Coffee is not so bad.
Caffeine works primarily by blocking “adenosine receptors” in the brain.
Adenosine leads to sleep pressure and blocking its receptors is one reason caffeine makes us feel more alert.
The source is very accurate in describing this important mechanism.
Coffee may also trigger gastric acid secretion and may lead to acid reflux, indigestion or stomach discomfort in poorly functioning individuals.
There is also a natural cortisol awakening response after waking.
Caffeine taken during this time compounds cortisol response by 30-50%.
That percentage should be treated cautiously and should not be presented as a universal effect.
The response to caffeine is very much a function of genetics, habit, sleep, medicine and physiology.
That is not to say you need to quit your morning coffee.
A more sensible routine is water first, coffee later.
Giving yourself at least 20-30 minutes after drinking water before having coffee is a practical thing if it is your routine, but there is no strong evidence that everyone medically requires this exact waiting period.
Protection from acid
Water can temporarily dilute gastric contents, lowering acid concentration.
However, the stomach regulates its acidity, and drinking water does not permanently neutralise gastric acid.
Stomach acid is essential for digestion, protein processing and microbial protection.
For a person with reflux, gastritis, ulcers or persistent upper abdominal symptoms, clinical assessment is much more important than water temperature.
Some prefer room-temperature or warm water for comfort, while others like cool water.
The key is adequate hydration, not the specific temperature.
Choose what feels comfortable for you.
Changes as we grow older
Hydration becomes more important with age since thirst perception and the body’s ability to conserve water can change.
Older adults may be more vulnerable to inadequate fluid intake.
The material also suggests that TRPM8 receptors are relatively preserved whereas vagal function declines with age, suggesting that cold stimulation may be more beneficial for older people.
And yes, this is an interesting biological theory but the claim that vagal function declines by about 1% every year or that TRPM8 compensates for this decline should not be taken as an established clinical rule.
The stronger and better-supported recommendation is much simpler i.e. when older people are having a problem, they should care for their hydration and not just rely on thirst.
What to do tomorrow morning
For most healthy adults, a morning detox ritual isn’t necessary.
Upon waking, it’s beneficial to drink a glass (250-300mL) of water before coffee or breakfast, choosing either cool or room temperature based on preference.
No additives like sugar, salt or detox powders are needed.
Water isn’t a treatment for heart disease, nor does it solve issues like high blood pressure or ageing.
Its primary value lies in replenishing what your body loses overnight.
The first drink of your morning does not need to be fashionable, expensive or complicated.
Start with water – before food, before coffee and before supplements.
The effect is quite simple:
You wake up after hours of not drinking water, so it is time to rehydrate.
Your stomach does not need a miracle every morning.
It needs you to treat it well.
That said, people with kidney, heart, gastrointestinal, metabolic or other medical conditions, or those who have been advised to restrict fluids, should follow the recommendations of their healthcare professional.
Datuk Dr Nor Ashikin Mokhtar is a consultant obstetrician and gynaecologist, and a functional medicine practitioner. For further information, email starhealth@thestar.com.my. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
