Lack of Sunlight
Sunlight has significant effect on how the body functions; it affects the pituitary gland that secretes melatonin, the hormone responsible for sleeping and waking cycles. There is a considerable lack of sunlight in winter, which impacts the internal body clock, affecting sleep cycles. Also, melatonin levels are high in winter; consequently, the body feels tired and drained, that's why we sleep more during cold weather.
Lack of Exercise
A regular exercise regimen is vital to boost energy levels. Deary weather is very demotivating for any exercise; even a short run in the cold is a chilly prospect. Lack of exercise makes us feel sluggish, lazy, and even obese, since no calories get burned. This leads to increased sleep during winter. Doctors suggest taking a brisk walk (even within the house will do) to increase body movement.
The Cold Air
The air is dry and cold during winters, and lacks moisture. The skin and nose are dry, and we tend to breathe through the mouth, leading to snoring and disrupted sleep. Also, heaters are continually on in winter. Heaters certainly warm up the room, however, the air in the room tends to get even more dry. Excess (and artificial) warm air dries out the internal mucus membranes, increasing vulnerability to bacteria, and consequently disturbed sleep patterns.
Different Eating Habits
Winters bring about an abundance of delicious, high-carb, sugary treats. The body naturally tends to trigger hibernation metabolism during these times, causing us to desire such foods. The hormone 'leptin' is associated with metabolism. Though digestion is better during winter, excess of fatty foods cause a change in the leptin levels of the body, leading to disturbed sleep. To get good sleep, avoid a very heavy dinner.
Cold winter days are characterized by oversleeping. It is completely normal to sleep more in winter; however, it is more of a sluggish tendency to oversleep and not get out of bed. Winters cause a change in the circadian rhythm, leading to fluctuating sleep patterns, and vice-versa. Too much or too little sleep affects the body. To avoid mental and physical exertion, avoid the tendency to oversleep, and try and regulate sleep patterns.
The House Temperature
Snuggling under the covers in front of the fire seems incredibly comforting during winter; however, a cooler room temperature promotes better sleep. On the other hand, a low room temperature in winter might cause one to shudder. Maintaining the right room temperature, between too hot and too cold, helps us sleep better in winter. Ideal room temperatures vary from person to person, though experts state that anything between 60 to 70°F is ideal.
The Season of Sickness
A depressing instance of how winter affects sleep is the onslaught of flu, colds, raging fevers, and other sicknesses during this type of weather. Chilly air affects the bones, especially among the elderly. Cramps, sore throats, etc., are no surprise. This creates a vicious circle - sickness prevents us from sleeping peacefully, but a sound sleep is necessary for the sickness to disappear. To sleep better, avoid physical exertion as much as possible.