The term leptin has been derived from the Greek word leptos, which denotes "thin". Leptin is basically a protein that is produced in the fat cells (also known as adipocytes) and it moves in the bloodstream finally reaching the brain. Since leptin is made by the fatty tissue in our body, it is natural that production of leptin will be more in people having more fatty tissue mass. A study undertaken on obese people found that people having more fat mass usually have four times more leptin compared to those who are not obese. The same study also confirmed the findings of an earlier study on the difference of leptin levels in males and females. It was found that the concentration of leptin was much higher in females compared to men. While researchers are yet to ascertain the reason behind this, it is believed that women have higher concentration of leptin because they posses larger amounts of fat mass in their body, mainly subcutaneous fat. In addition, the impact of sex steroid hormones also contributes to the high leptin production in their body. As the amount of leptin produced by one's body reveals the body fat amount in an individual, it is perhaps a rational explanation that the production of this hormone is different in males and females.
Precisely speaking, leptin is a type of 16Kda protein hormone. It is made in the body's fat cells. Leptin plays a number of roles in our bodily functions and it is mainly associated with regulating our body weight by working together with the region of the brain known as hypothalamus. Below are a few instances that show the importance of leptin in maintaining our physical health and also how this hormone functions in our system.
Researchers first discovered the presence of leptin towards the end of the twentieth century. This hormone circulates in our bloodstream to reach the hypothalamus in the brain. Inside the hypothalamus, leptin works on particular neurons or nerve cells and regulates our appetite. Leptin generally activates the hypothalamus by transmitting signals which allow the body to be aware that there is no hunger at that particular time and, hence, the body desists from eating any food. Since leptin plays an important role in regulating the degree as well as frequency of hunger experienced by the body, this hormone helps to diminish the body’s craving for food. However, it is worth mentioning here that leptin does not have any effect on our emotional desire for eating sweets and several other types of foods.
Although protein hormones are known to perform their functions effectively, in no way do they make certain that people will not consume foods more than they need to maintain a healthy balance. In addition, nor can the chemical reactions of leptin inside the body regulate the food types that an individual will eat from time to time. Looking at leptin from this viewpoint, an individual can as well prefer to ignore their feeling of hunger and also opt for any snack or even taking a second helping while taking his/her meal. In such situations, the additional food consumed by an individual is transformed into energy and stored inside the body in the form of fat. Over a period of time, it is possible that the surplus fat stored in the body will make leptin's ability to regulate appetite further difficult. This is because our body will no more be able to clearly read and differentiate between the brain’s hints to desist and cease.
Leptin's presence in our system helps us to naturally sense when the body does not need to consume extra food. Leptin actually helps us to follow and understand the signals transmitted from the hypothalamus of the brain. In addition, this protein hormone also helps us to select the type of food we ought to consume and puts a ceiling on the amount of food we should eat to maintain a healthy body and mind. In fact, if we were able to follow all the suggestions sent from the hypothalamus in this connection precisely, we would certainly have lesser problems related to body weight and remain physically fit. We are fortunate that it is possible to train our minds afresh so that we are able to pay heed to the physical suggestions that start as soon as leptin is produced in our system. By doing so, we can certainly alter our eating habits so that the body produces sufficient energy needed by it to undertake all functions effectively on a regular basis.
Leptin is also beneficial for thin people having too little body fat. Such people can gain from leptin which helps to control their body weight by means of regulating their appetite as well as making the optimum use of energy stored in their body. On the other hand, people who have excess body weight can often face problems if the concentration of leptin is high in their bloodstream. Elevated level of leptin in overweight people's bloodstream can result in health conditions like anorexia (absence of appetite), obsession with food, bulimia and even a sluggish metabolic process.
In the beginning, it was thought that fat tissues in the body released leptin and its circulation in the bloodstream depended on the total quantity of fat tissues in one's body. However, this perception has changed and now it is believed that this hormone has multiple functions and it produced by a variety of organs and tissues in our body, including the kidneys, stomach, placenta and even the salivary glands.
It is important to note that leptin is among the four major hormones in our body that are responsible for our body weight. The synthesis of this hormone takes place in the fat tissues in our body, while higher concentrations of leptin receptors are found in the hippocampus and hypothalamus regions of the brain. The production of leptin is directly proportional to our body’s fat content. Therefore, individuals having more body fat will produce more leptin. Various organs and tissues produce leptin and release it in our bloodstream, which transports this protein hormone to the brain. In the brain, it transmits satiety or fullness signals to the brain’s hypothalamus region.
In fact, leptin lets the brain know that sufficient amount of fat is stored in our body and, hence, there is no need to consume additional food. This, in turn, helps us to burn calorie in a normal manner.
It has been established that people who chronically have a high concentration of leptin in their bloodstream are most likely to suffer from one or more conditions like overeating, obesity as well as inflammation-related ailments such as hypertension, heart disease and metabolic syndrome. Some people may also suffer from leptin resistance - a condition that results in the arteries becoming hardened. Leptin resistance also has an adverse effect on the growth of our bones and blood vessels, the reproductive system as well as the immune system.
In general, leptin has a vital role in controlling our food intake, regulating our body weight and maintaining a healthy balance of energy. In addition, leptin also plays a part in controlling other hormones' functions. The hormones whose functioning leptin regulates include those secreted in the pancreas, adrenals, thyroid glands and even those related to our sexual activities. Leptin has various other purposes, such as regulating the areas of the brain that keep an eye on the thyroid levels, osteoporosis, diabetes, aging, heart ailments and also helps to control the sympathetic nervous system, which is associated with our blood pressure.
However, leptin's primary function in our body is to regulate hunger or control our appetite, but telling us when, what and how much we should eat.
In fact, leptin works on the hypothalamus - the region of our brain that regulates hunger as well as the feeling of satiety after a meal. The function of leptin is to send signals to our brain to reduce hunger since the body already has a sufficient store of fat. As a result, we consume less food. Leptin is also known as "anti-starvation hormone" as low concentration of this protein hormone results in augmented appetite. In a nut shell, people with elevated levels of leptin take lesser food because they feel less hungry.
Similarly, when the storage of fat in our body is less (for instance when we diet), the levels of leptin in our bloodstream too decreases. As a result, the hypothalamus sends signals to enhance appetite and we feel hungry. This often leads to excessive consumption of food, thereby increasing the storage of fat in our body. When the body has more fat, it results in production and release of more leptin. When the body has stored sufficient amount of fat, leptin informs the hypothalamus to decrease appetite - resulting in lesser intake of food. This, in fact, is a typical negative feedback method.
To some extent, leptin also regulates our body temperature as it has an impact on metabolism by means of communication with the thyroid glands. Similarly, leptin also invigorates our immune system. When we are affected by any infection or suffer from inflammatory stimuli, for instance LPS (lipopolysaccharide) caused by bacteria, cytokins and turpentine, the levels of leptin rise in the bloodstream.
Leptin receptors are present in neutrophils, B as well as T lymphocytes and monocytes - suggesting that this protein hormone helps in regulating these immune responses. It has been found that leptin can increase the stimulatory performance of LPS on activation and proliferation of human monocytes. This protein hormone also enhances oxidative stress (imbalance between the harmful free radicals and antioxidants in the body) in macrophages. On the other hand, it reduces oxidative burst or respiratory burst in monocytes that have been activated earlier.
Leptin may also function as macrophage/monocyte chemo attractant. In other words, this protein hormone has the ability to draw the immune cells to any local area.
