To produce and maintain body heat, humans and other warm-blooded animals produce heat through energy metabolism in a process known as thermogenesis. Although thermogenic heat is a byproduct of physical activity and food digestion, the main production for cold adaptation occurs in brown adipose tissue. As such, finding ways to boost thermogenesis and energy production, such as vitamin A supplementation and exposing oneself to cold environments may also impact body composition.
Brown and White Adipose Tissue
There are two main categories of adipose tissue: brown and white. White adipose tissue stores excess calories and excretes leptin and other hormones. This consists of the vast majority of adipose tissue in adults and is associated with the more detrimental aspects of obesity.
Conversely, brown adipose tissue is beneficial, as it aids in thermogenesis and fat metabolism. Researchers looking to manage obesity and related disorders search for ways to support brown adipose tissue and reduce white adipose tissue, including by converting white adipose tissue to brown.
New research has also designated the third type of adipose tissue as beige, which is a blending of the two types. This occurs when brown adipose tissue accumulates in white adipose tissue. As with brown adipose tissue, this beige tissue produces more energy and burns calories through thermogenesis.
There are some diet and lifestyle actions (such as exposing oneself to cold temperatures and vitamin A intake) that may potentially help convert white adipose tissue to brown or beige, a process known as “browning” or “beiging.”
Vitamin A Stimulates “Browning”
Vitamin A plays an important role in whether adipose tissue is brown, white, or beige, especially in cold temperatures. A recent study demonstrated the role of cold temperatures in mitigating the influence of vitamin A on adipose tissue as a way to regulate cold adaptation, which in part relies on additional brown adipose tissue for increased thermogenesis. Vitamin A aided in the increase of thermogenic gene expression and energy metabolism, stimulated by the cold temperatures as part of adaptation to the environment.
Retinoids, the group of molecules known as vitamin A, act as signaling molecules. Vitamin A stores reside in the liver, and cold temperatures stimulate the liver to redistribute vitamin A into adipose tissue. The plasma retinol transporter retinol-binding protein (Rbp) mediates the secretion and transport of retinol into adipose tissue. In this study, the mice who did not have the Rbp also did not have the same cold-mediated changes to their adipose tissue, demonstrating the importance of vitamin A and retinol supply to this adaptation.
The impact of vitamin A on “browning” or “beiging” may be due in part to the all-trans retinoic acid’s altering of the mitochondria to increase the ability for energy metabolism. Regardless of the exact mechanisms, a previous mouse study found an inverse relationship between dietary vitamin A levels and brown adipose tissue, demonstrating the importance of vitamin A to regulate it.
Stimulating browning may be one additional role vitamin A plays in the body, along with its importance in eye health, immune health, reproduction, and antioxidant capacity. Therefore, ensuring adequate vitamin A levels with diet and supplementation may provide a wide range of health benefits. However, excess vitamin A supplementation may be toxic, so discuss the right dosage for your situation with your health-care practitioner, nutritionist, dietician, or health-care team.
By Kendra Whitmire, MS, CNS