Leptin is a vital hormone in the human system that plays a key role in controlling hunger and appetite, besides promoting optimal energy and fat metabolism in the body. Also known as the “satiety hormone” or “starvation hormone”, leptin regulates eating patterns and portions so as to prevent an individual from both extremes - eating very less and overeating. In fact, in persons who are overweight and those suffering from obesity, one of the primary factors is attributed as large amounts of leptin in the body which is not detected by the brain – a condition termed as leptin resistance, which is similar to type 2 diabetes mellitus, wherein insulin resistance develops in the system.
In the human body, leptin is synthesized by the fat cells, referred to as adipose cells or lipocytes situated in adipose tissue. Adipose tissue is located all over the body, including under the skin as subcutaneous fat to provide insulation from heat and cold, surrounding internal organs of eyes, kidneys, liver, stomach, intestines, heart, lungs as visceral fat to serve as a cushioning layer of protective padding, as well as in between muscles, bones and joints. Thus, the more body fat the system possesses, the more leptin is produced. Leptin is then released from fat cells in adipose tissue into bloodstream, wherein it traverses to the hypothalamus in the brain and exerts its effects.
When an individual eats food, body fat increases and leptin levels are elevated, thus signaling the system to consume lesser quantities of meals and burn more calories. Likewise, when a person is not eating food, body fat levels tend to drop which decreases leptin concentrations, inducing the system to ingest more meals and burn less calories. Hence, the leptin hormone performs the crucial task of maintaining normal body weight and preventing unhealthy weight gain and extreme weight loss. While leptin does not directly influence the amount of food or portion size with every meal, it plays a pivotal role in regulating body fat levels and energy metabolism over a period of time.
Leptin And Its Structure:
Beginning from 1950, numerous scientific teams conducted research on obese mouse models to understand the mechanisms behind massive fat gain by the human body. Eventually, it was the renowned American biochemist Douglas L. Coleman and the reputed American molecular geneticist Jeffrey M. Friedman who discovered the leptin hormone as well as the gene encoding for it, known as the ob gene, in the year 1994.
For their groundbreaking discovery of leptin hormone and the ob gene, Coleman and Friedman were conferred several prestigious awards in the domain of bioscience and biomedical research. Furthermore, in the year 1995, it was confirmed that leptin receptors were situated in the hypothalamus region of the brain, which was associated with influencing the sensation of hunger, as well as regulating body weight. Leptin also interacts with other hormones in the body, including insulin, glucagon and the growth hormone, indirectly mediating their actions on hunger perception and energy metabolism.
The ob (lep) gene – where ob denotes obesity and lep stands for leptin, is located on chromosome 7 in the human system. It encodes for the leptin hormone, which is a cytokine protein composed of 167 amino acids arranged in a long chain with four helical assemblies. Leptin has a molecular weight of 16 kDa (kilo Daltons – with Dalton being a central unit of atomic mass).
Functions Of Leptin:
Leptin is involved in myriad important functions in the body, including:
- Regulating body weight, calorie/energy expenditure and fat metabolism
- Uplifting immune system activity to defend the body against chronic diseases and infections
- Increasing bone mass and strengthens muscles, joints
- Preserving reproductive hormone levels so as to ensure timely ovulation and healthy pregnancy in women
- Fostering the onset of puberty and optimal sexual wellness in adolescents – boys and girls
- Augmenting cardiac muscle strength and heart wellness
- Enhancing lung capacity and respiratory health
Adverse Effects Of Hormonal Imbalance In Leptin:
Low levels of leptin lead to extreme overeating and childhood obesity, since the hypothalamus in the brain is not stimulated by leptin and thus does not activate the hunger response and appetite control mechanism. This is caused by a rare condition known as congenital leptin deficiency that is present in babies right from birth and can be treated with hormonal therapy by means of leptin injections, that triggers massive weight loss and reverses childhood obesity.
High levels of leptin invariably lead to obesity. Since the brain does not respond to an increase in leptin levels in blood circulation owing to leptin resistance, the adipose cells continue to produce leptin and the body senses constant hunger that leads to overeating and huge fat stores in the system.