Brown fat, or brown adipose tissue, is a specialized type of body fat that functions as a personal heater for newborns. Unlike white fat, which stores energy from calories, brown fat’s purpose is to generate heat. This tissue is abundant in infants, helping them manage the temperature change after birth. Its presence is an important feature for a baby during the initial months of life.
The Function of Brown Fat in Newborns
The primary role of brown fat is to produce heat through a process called non-shivering thermogenesis. This is important for newborns because they lose heat rapidly and have not yet developed sufficient muscle to generate warmth by shivering. Brown fat bridges this gap, allowing them to maintain their core body temperature when exposed to cooler environments.
This heat-generating tissue is located around the back, neck, and shoulders. Additional deposits are near the kidneys and other organs, warming the blood that circulates through these areas to protect the baby’s core from cold.
The composition of brown fat differs from white fat. White fat cells contain large droplets of lipids for energy storage. In contrast, brown fat cells are packed with mitochondria, which are rich in iron and give the tissue its characteristic color. These mitochondria are the cellular powerhouses that enable brown fat to burn calories and produce heat.
Development and Reduction Over Time
The development of brown fat begins during the final trimester of pregnancy. This prenatal accumulation is timed to prepare the infant for the thermal stress of birth. Consequently, premature babies often have insufficient stores of brown fat, making them more susceptible to cold stress and requiring temperature regulation in a neonatal intensive care unit.
As a baby grows, the amount of brown fat naturally decreases. This reduction typically begins during early childhood and continues into adolescence. By the time a person reaches adulthood, only small amounts of brown fat remain, primarily around the neck, kidneys, and spinal cord. This decline is a normal part of development as other heat-regulating mechanisms mature.
The diminishing reliance on brown fat is directly linked to the development of other bodily systems. As an infant’s muscle mass increases, they gain the ability to shiver, providing a new method for generating heat. Simultaneously, they accumulate more white fat, which acts as an insulating layer, reducing heat loss from the body.
How a Baby’s Body Uses Brown Fat
The activation of brown fat is an automatic response triggered by cold. When a baby’s body senses a drop in temperature, the nervous system releases a hormone called norepinephrine. The brown fat cells have receptors that detect this hormone, initiating the heat-production process within the tissue. This response ensures the baby can counteract the cold before their core temperature drops significantly.
Once activated, the mitochondria within the brown fat cells begin to burn fatty acids at a high rate. This metabolic process generates a substantial amount of heat directly within the tissue. As blood flows through these active brown fat deposits, it is warmed and then circulated throughout the rest of the body, raising the infant’s overall temperature.