Feeling cold when the sun goes down is a common experience. This nightly chill is usually not a cause for concern but rather a sign that the body’s internal systems are preparing for sleep. The sensation of coldness is connected to the body’s 24-hour internal clock, which regulates physiological functions, including temperature. This natural process involves intentionally lowering the body’s core temperature to promote rest. However, persistent or excessive coldness may suggest an underlying health issue interfering with normal temperature regulation.
The Natural Drop in Core Body Temperature
The primary reason for feeling cold at night is the body’s biological imperative to initiate sleep, which requires a drop in internal temperature. This process is governed by the circadian rhythm, the internal 24-hour cycle that dictates wakefulness and sleep. The suprachiasmatic nucleus (SCN), a small area in the hypothalamus of the brain, acts as the master clock, signaling the body to adjust its temperature as evening approaches.
The SCN cues the body to lower its core temperature by approximately 1 to 2 degrees Fahrenheit (about 0.6 to 1.1 degrees Celsius) as part of the transition into sleep. This reduction begins in the late afternoon and continues until the body reaches its lowest temperature about two hours before waking up. This temperature drop is a necessary precondition for the onset of deep, restful sleep.
The body achieves this cooling by decreasing its metabolic rate, which reduces internal heat production. This temperature shift is considered a physiological gateway for sleep, making the body more conducive to rest. The physical mechanisms the body uses to shed this heat are what create the noticeable feeling of coldness.
Physiological Mechanisms of Heat Loss
The body executes the necessary core temperature drop by actively pushing heat away from the center and toward the periphery. This is accomplished through a process called vasodilation, where blood vessels, particularly those near the surface of the skin in the hands and feet, widen. This increase in peripheral blood flow brings warm blood closer to the skin, where the heat can more easily dissipate into the cooler surrounding environment.
As warm blood flows to the extremities, the skin temperature of the hands and feet temporarily rises. This heat transfer allows the core temperature to fall, but the rapid loss of heat from the skin surface triggers the sensation of being cold. The body radiates its internal warmth outward to cool the core.
The feeling of coldness can be intensified by the surrounding environment, as a cooler room accelerates this natural heat loss. If the bedroom temperature is too low or the bedding is too thin, the body sheds heat faster than intended. This can lead to the unpleasant sensation of shivering or being excessively chilled, even though the body is simply performing its nightly thermoregulatory task.
Underlying Medical Causes of Nighttime Coldness
While a mild chill is normal, excessive or persistent coldness at night may signal that a medical condition is impairing the body’s ability to generate or regulate heat. One common cause is anemia, characterized by a low number of healthy red blood cells or a lack of hemoglobin. Since red blood cells transport oxygen, a deficiency means less oxygen is delivered to tissues, impacting their ability to produce heat and causing coldness, particularly in the hands and feet.
Another factor is hypothyroidism, where the thyroid gland does not produce enough hormones. Thyroid hormones regulate metabolism, and a shortage slows this process, leading to a drop in the body’s overall heat generation. People with an underactive thyroid often report feeling cold more than usual, even in warm environments.
Poor circulation, often linked to Peripheral Artery Disease (PAD), can also contribute to nighttime coldness. If arteries are narrowed or blocked, the body struggles to move warm blood to the extremities, leading to persistently cold hands and feet. Certain medications, such as beta-blockers, can also interfere with temperature regulation by reducing blood flow to the skin. If the cold sensation is severe or accompanied by symptoms like fatigue or unexplained weight changes, consulting a healthcare provider is recommended.