What is Leptin, and what Stimulates Leptin Secretion
The term LEPTIN is derived from a Greek word called “leptos,” which means “thin”. The adipose tissue (fat cells) of your body produces leptin. White Adipose Tissue (WAT) serves as the primary source of leptin. But, there exists evidence that other tissues like Brown Adipose Tissue (BAT), placenta, and ovary also produce leptin hormone.
The leptin hormone is produced in a pulsatile rhythmic pattern with higher secretion during the nights and early morning hours. The circulating leptin level in the bloodstream directly reflects the amount of energy stored (fat reserves) in your body. The leptin receptor cells circulate throughout the hypothalamus and cerebellum of your brain, thus detecting circulating leptin concentrations.
The hormone works on a negative feedback loop where leptin levels, when detected by the receptors, signal the CNS to regulate the food intake. This working does not happen just for one meal a day, but a continuous cycle throughout your body’s lifetime.
Leptin resistance and sleep have a correlating relationship, and we will continue below of how they are related and how sleep apnea can contribute to throwing this important hormone off.
What Leptin Does in your Body
Lipostat becomes the primary function of leptin. Signaling or communicating with other body systems about the available energy reserves is one of the important roles that leptin carries out in your body. In addition to signaling, catalyzing the fuel (energy) consumption and mobilization are other roles of the leptin hormone. In short, leptin is a hormone involved in many functions of your body.
This research paper deeply investigates leptin’s interaction with other metabolisms, hormones, growth hormone axis, cytokines, and insulin & insulin sensitivity. With these insights of leptin interaction, researchers have well-studied the hormone’s in and out functions and how foods can affect it as well.
Apart from leptin’s microscale functions in signaling, researchers have found the prominent functions of leptin in energy regulation (energy homeostasis), metabolisms, and other endocrine functions.
The concentration of leptin in the bloodstream acts as an energy gauging system in your body. When the leptin receptors detect these leptin levels in your brain’s hypothalamus, a complex CNS circuit activates.
This initiates either the anorexigenic (appetite-diminishing) or orexigenic (appetite-stimulating) activities that control food intake. In simple terms, the leptin energy gauge signals the central nervous system (CNS) to regulate the food intake and respective energy expenditure processes. Thus, it makes the hormone exert an immediate effect on brain function in terms of appetite.
Other secondary functions of leptin include,
- Regulation of immune function
- Bone metabolism
- Decreased levels of reproductive hormones
- Appetite for pregnant women and the fetus
- Decreased levels of thyroid-stimulating hormone
- Lower activity of the growth hormone
The research on leptin’s peripheral actions and interactions discussed above also studied the wider roles of leptin other than energy homeostasis. This includes,
- Acting as a growth factor for particular cell types
- Regulation between the fetus and the maternal metabolism
- Mediating the energy expenditure process
- Acting as a permissive factor for puberty
- Interactions with other hormones and factors like insulin, glucagon, the insulin-like growth factors, and glucocorticoids
- Multiple roles as endocrine, paracrine, and autocrine factors
In-depth studies were undertaken to understand the role of leptin concerning puberty in adults. It’s found in the studies that leptin plays an important role in regulating the onset of puberty. The results showed that undernourished and thin women take a longer time to reach puberty than other women. Also, these women may suffer from unhealthy ovulation processes that affect the egg’s release during the menstruation cycles. This, in turn, affects reproductive growth and the process of reproduction in the body.
So, How does Leptin Hormone Regulation relate to your Sleep?
As leptin production greatly depends on the lipid cells (fat cells), the body fat becomes the primary regulator of the leptin hormone. An obese (fatty individual) shall have a higher concentration of leptin in their bloodstream. In contrast, an individual with lower fat (lower BMI) may have a lower leptin concentration in their bloodstream. However, these concentrations may result from a long period and not just a one-time or one-day implication.
Also, as leptin production follows a circadian rhythm like other hormones in your body, sleep may affect leptin concentrations in the bloodstream. The relationship between sleep and leptin levels are discussed in detail in the latter part of the article. Stay tuned for the surprising facts and results that researchers have found on how sleep or rather sleep disorders like sleep apnea can affect your body!
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What is Leptin Resistance:
In healthy individuals and under normal conditions, the abundance of leptin in the bloodstream must signal the brain and the body to reduce the food intake, thus lowering the appetite. This makes the body utilize the available fat reserves for energy expenditure and keeps up healthy body weight.
But, obese people will have abnormal (high) levels of leptin in their bloodstream. This makes their body resistant to the high levels of leptin and develops a condition called “Leptin resistance.” In this state, the brain will neither respond to the higher leptin nor signal the body for lesser food intake or decreased appetite. When this resistance persists, the severity increases and results in adverse obese conditions. This, in turn, may lead to a further increase in the production and release of leptin in the bloodstream. Diet and quality sleep play a large role and work together to help regulate leptin and keep it balanced.
Experts suggest that the leptin resistance might have been caused due to inflammatory signaling between the leptin molecules and the leptin receptors in the hypothalamus, and higher levels of free fatty acids that interfere in signaling.
Lower levels of leptin in the body signal for an increased food intake condition in both adults and children. The body senses the lower leptin levels signaling from the lack of fat reserves, thus leading to appetite.
In children, the persistence of this condition may lead to a state of childhood obesity. This becomes severe when the increased food intake continues over several years. In some children, this leptin deficiency causes a delay in the onset of puberty. Due to these consequences, the affected children may generally have poor immune systems and may further contract other body/metabolic disorders.
Now here’s How Sleep affects your Leptin levels..
You already knew that sleep plays a vital role in maintaining the energy homeostasis within your body. To manage your diet (food intake) and weight, you need to have a sound sleep regimen (enough sleep of 7-9 hours) every day at the same time. In contrast, any changes to the sleep cycle, sleep time, and sleep duration may greatly affect the food intake and, in turn, the energy homeostasis.
In general, lack of sleep affects the body in two ways:
- One with a rise in the lipid levels (endocannabinoid) in the bloodstream. This lipid acts like marijuana that stimulates your appetite, especially in the evening, when food intake should be reduced.
- Others are related to the rise in the satiating hormones, namely leptin, and ghrelin. When your body lacks sleep, leptin levels fall, and ghrelin levels increase. Both lead to an increase in appetite.
A fundamental and strong association between sleep apnea, other sleep disorders, and leptin may develop due to the circadian rhythm. Sleep follows a diurnal circadian cycle, and the release of leptin shows a strong circadian rhythmic pattern.
Like cortisol and other hormones that get affected due to change in the circadian rhythm, leptin concentrations vary with the circadian pattern. Higher concentrations of leptin in the bloodstream occur at the onset of the evening or at night (when the sleep cycle initiates), and lower concentrations occur during the day (wakefulness).
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While there are numerous research and empirical studies, some scientists suggest that the change in the hormone levels during sleep may have occurred due to evolution.
For years, it’s believed that long nights occur during winter, and short nights occur during summer. It has become a mindset that winter (long nights) relates to little food and summer (short nights) relate to food abundance. This may arise due to extended sleep with longer nights, leading to higher leptin levels and a less amount of sleep with shorter nights, leading to low leptin levels. Hence, the body prepares itself to burn the calories already stored during winter and take in food as much as possible to save the calories during summer.
The relationship between sleep and leptin levels was well studied in a research study. Perhaps, this research paved the way to numerous other studies that went deep into finding the association of leptin and sleep.
This study found that sleep was inversely proportional to BMI. A decreased sleep (less than the nominal 8 hours) showed increased BMI (obesity, a condition where leptin levels are pretty low). The study also clearly revealed the association of decreased leptin to deprived sleep observed in real-life conditions, unlike the previous studies that were experimental and performed under controlled laboratory conditions. Thus, this study proved the impact of sleep over leptin levels and appetite.
Another study dealt with the relationship between sleep and leptin concerning the central nervous system activities. It proved that decreased sleep might affect the bloodstream’s leptin levels due to an inhibitory effect by your body’s CNS. An increased sympathetic outflow hindering the leptin release was one of the two major findings in this study. The second finding relates to the association of sleep restriction with not the leptin levels, but the amplitude of the leptin rhythm. A decreased sleep routine led to a reduction in the amplitude of the leptin rhythm.
It was also found that leptin levels may increase even when sleep occurs in the daytime apart from the regular sleep at night. This again proves the regulation of leptin levels by sleep. Alternatively, sleep restriction may lead to decreased leptin levels that cause appetite, which increases wakefulness in some patients.
Association between Sleep and Leptin Levels in Children
A research study that analyzed the association of sleep duration with the hormone leptin among children and adolescents revealed that children who had sleep restrictions or slept less than the U.S. National Sleep Foundation recommendation levels showed no influence over the leptin levels. These surprising results led to a higher curiosity among the researchers and made them undergo in-depth studies to clearly understand the relationship between sleep loss and leptin levels in children or infants.
Leptin in conclusion
Though disparity exists between empirical studies, none can deny the fact that sleep plays an important role in not just maintaining the leptin levels but majorly regulates the energy homeostasis, metabolism, and other neuroendocrine functions. Hence, having an adequate sleep routine becomes the priority for children and adults to maintain their weight and food intake keeping their body in homeostasis for health and longevity.