By Dr Khumo Merafe
With winter comes an increase in absenteeism, flu cases, and declining employee morale. The response is often predictable: flu vaccine campaigns, reminders to wash hands, and wellness newsletters encouraging healthier lifestyles. These initiatives are important, but they assume that winter is primarily a behavioural challenge; it isn’t. Winter is a physiological event.
As Stanford neuroscientist Dr Andrew Huberman observes, “Morning daylight synchronises gut motility, glucose control, appetite hormones and sleep. The most underrated metabolic tool we have.” Yet during a South African winter, many employees leave home before sunrise, spend the day indoors, and return home after sunset. Long before someone develops the flu, their biology has already begun responding to seasonal change.
The later sunrise, colder temperatures, reduced sunlight, and changes in human behaviour all influence how the body regulates sleep, mood, immunity, appetite, cardiovascular function, and energy. In other words, winter changes how employees think, feel, and perform long before they become ill. Understanding this allows HR managers to move beyond reactive wellness initiatives and instead build workplaces that work with human biology rather than against it.
The first change happens before employees even arrive at work. Human beings operate on an internal 24-hour clock known as the circadian rhythm, regulated primarily by light exposure. Researchers consistently identify light as the strongest external regulator of the human circadian clock, influencing melatonin release, alertness, and sleep-wake timing. Morning sunlight tells the brain that it is daytime, suppressing melatonin and increasing alertness. During winter, however, the sun rises later and many people begin their commute before receiving adequate natural light. The result is delayed wakefulness, slower morning cognition, and the familiar feeling of “brain fog”.
The employee struggling to get going at 8 AM is not necessarily unmotivated. Their biology is responding to a seasonal change. Encouraging morning outdoor breaks, allowing flexibility where operationally possible, and promoting healthy recovery habits can help employees align with these natural rhythms.
Winter also affects moods. Reduced sunlight influences serotonin pathways involved in motivation, emotional regulation, and overall wellbeing. At the same time, longer periods of darkness extend melatonin production, contributing to fatigue and sleepiness. Employees may appear withdrawn, less engaged, or less productive when they are, in fact, experiencing the biological effects of reduced daylight.
Seasonal mood changes are well documented, with reduced energy, social withdrawal, and fatigue among the recognised features experienced by many people during darker months. What HR may interpret as disengagement or poor attitude may, in some instances, be physiology interacting with the environment.
Mental health support during winter should therefore be viewed as preventative healthcare rather than crisis management. Regular check-ins, manager awareness, and opportunities for employees to spend time outdoors during daylight hours can make a meaningful difference.
Another commonly overlooked change is appetite. Many people become frustrated with themselves during winter because they crave bread, pasta, sweets, and other comfort foods. In fact, increased appetite—particularly for carbohydrates—is a recognised feature of winter-pattern seasonal mood changes. While personal choices remain important, biology also plays a role.
Changes in serotonin signalling and evolutionary energy-conservation mechanisms can increase the drive for high-calorie foods during colder months. Historically, this may have served as a survival advantage. In today’s workplace, however, those same biological tendencies meet office birthday cake, vending machines, and convenient takeaways. Unfortunately, modern workplaces often compound the problem by surrounding employees with convenient but unhealthy options.
HR managers can support healthier habits by making nutritious choices more accessible in the organisational canteen, rather than relying solely on willpower.
Winter also places additional strain on the cardiovascular system. Cold temperatures cause blood vessels to constrict, increasing vascular resistance and raising blood pressure, placing greater demand on the heart, particularly for employees living with hypertension or other chronic conditions. Workplace wellness initiatives should therefore include preventative health screenings, blood pressure monitoring, and education around medication adherence during winter months.
Finally, winter changes how people move. Colder weather, darker mornings, and shorter days naturally reduce physical activity, contributing to lower energy expenditure, poorer metabolic health, and worsening fatigue. Rather than expecting employees to find motivation after hours, organisations can design movement into the workday through walking meetings, step challenges, or scheduled activity breaks.
The most effective HR departments understand that employees do not leave their biology at the office door. Winter influences how people sleep, move, eat, recover, and think. It influences mood, cardiovascular health, appetite, energy, and ultimately workplace performance. Organisations that recognise these physiological realities will not only have healthier employees but also more resilient teams and stronger organisational performance.
Winter is not simply a season. It is a biological event.
Dr Khumo Merafe
