For most people, caffeine is a reliable daily companion. But for a growing number of adults, the same cup of coffee that sharpens focus in the morning is also behind jitters, disrupted sleep, or afternoon anxiety they can’t adequately explain. Understanding it comes down to a surprising piece of biology: how your body actually processes caffeine.
Metabolism factor
Caffeine is mainly metabolized by the liver enzyme CYP1A2. The rate at which this happens varies considerably between people. This is mainly determined by genetics. Research in Genetics of nature identified variants in the CYP1A2 and AHR genes as major determinants of caffeine consumption and sensitivity.
Broadly speaking, about 40% of people are fast metabolizers, clearing caffeine quickly with minimal side effects. About 50% fall into the middle category. And about 10% are slow metabolizers, where even moderate consumption can cause noticeable and long-lasting effects. These include insomnia, nausea, and increased heart rate.
This genetic variation also explains why caffeine sensitivity is not static. It increases with age as liver metabolism slows, sleep architecture changes, and the body becomes more efficient at clearing stimulants.
For women in perimenopause and menopause, hormonal changes add another layer. In fact, research from Mayo Clinic has associated caffeine consumption with more and more troubling vasomotor symptoms. These include hot flashes and night sweats in this population.
Sleep connection
Perhaps the most well-documented effect of caffeine is its effect on sleep—and it’s more important than most people realize.
Caffeine works by blocking adenosine receptors in the brain. Adenosine is a neuromodulator that builds up during the day to create a sleepy feeling; by binding to its receptors, caffeine effectively delays this signal. The problem is that caffeine’s half-life in the body is typically five to six hours. This means that mid-afternoon coffee has half its stimulant load in your system.
Important research
Important research published in the journal Journal of Clinical Sleep Medicine fConsuming caffeine 6 hours before bed reduces total sleep time by more than an hour.
Now that’s important!
Given that insufficient sleep is associated with impaired cognitive performance, elevated cortisol, increased appetite, and long-term cardiovascular risk, the downstream effect of midday caffeine consumption is unlikely. Ultimately, it can affect your longevity.
Change in consumption patterns
These findings are increasingly reflected in consumer behavior. Market research from Euromonitor International and Mintel shows continued growth in the herbal and decaffeinated tea categories worldwide. This is partly due to the increased focus on sleep quality and evening wellness practices.
Transitioning isn’t about abstinence – it’s about timing. Many adults enjoy caffeinated beverages in the morning and afternoon, switching to caffeine-free alternatives as the day progresses.
One option that is gaining traction in this space, especially in South Africa, is rooibos. Naturally caffeine-free, rooibos has attracted scientific attention beyond its prominent role as a stimulant substitute.
Longevity benefits
Rooibos tea (pronunciation chief) is a popular caffeine-free herbal infusion made from the leaves of the Aspalathus linearis shrub. Although commonly referred to as “red tea” or “red bush tea”, it is not true tea because it is not traditionally obtained. Camellia sinensis tea factory
Rooibos is unique to South Africa, meaning it does not grow naturally anywhere else on earth. Due to its geographical connections, the name “Rooibos” has a Protected name of origin (PDO) status in the European Union.
Cortisol response
Preliminary research has explored the herb’s potential effects on the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the body’s cortisol response. Research conducted in Phytomedicine They found that aspalatin and notofagin—two key flavonoids found in rooibos—may help regulate cortisol secretion, although the researchers note that larger human trials are needed to confirm these effects.
How many cups of coffee is too many?
Health authorities, including the European Food Safety Authority and the US FDA, generally consider up to 400mg of caffeine a day – about four cups of coffee – to be safe for healthy adults.
But “safe” and “best” are not the same thing, and individual sensitivities vary considerably. For those who are slow metabolizers, in hormonal transition, or simply notice that their sleep is lighter than before, cutting back on late-day caffeine intake is one of the most evidence-based adjustments available.
The broader principle is simple: caffeine at the right time is a useful tool for your biology. Consumed too late or in excess of your metabolic capacity, it works against the very health outcomes most people are trying to support.
A final note
Paying attention to when and how much caffeine you consume is a cost-effective and effective place to start. Consider if you are taking too much for your personal metabolic constitution. Balancing your caffeine intake is an important health habit. Today we have many options like rooibos, or matcha or a wide host of other herbal beverages are available to provide the same taste pleasure.
