Written by: Kevin Cann
Our body is an interconnected web of checks and balances. Our total health relies on this state of natural balance. Part of this natural balance is our circadian rhythm. We follow approximately a 24 hour sleep-wake cycle. This would still be true if not one clock existed on earth. This sleep-wake cycle is responsive to light. This is why it is so important to sleep in a completely blacked out room and to not have a lot of artificial light stimulation before bed. It confuses our body into thinking it is still daytime and throws off our natural balance. A piece of our hypothalamus, approximately the size of a grain of rice, plays a major role in maintaining this natural balance.
This piece of our hypothalamus is known as the suprachiasmatic nucleus (SCN). Our SCN is in charge of our circadian rhythm. It communicates with the rest of the body to keep it on a 24 hour schedule. However, it tends to be a little off at times and needs environmental cues such as light to reset it and keep it in sync with the environment. This is more than likely due to us evolving on planet earth.
Our sleep-wake cycle is not the only thing that follows a circadian clock. Other functions such as alertness, hormonal levels, and immune function all work off of our circadian rhythm. The SCN therefore plays a major role in the control of almost all of our daily functions. Neurotransmitters play a critical role within the SCN.
Histamine is a neurotransmitter that plays a role in immune function. It also may play a major role in maintaining circadian rhythm. Some studies suggest that histamine is the final neurotransmitter involved in the process of resetting our biological clock (http://www.ncbi.nlm.nih.gov/pubmed/10918634 ).
Serotonin plays a role within the SCN to modulate the “pacemaker” response to light (http://www.ncbi.nlm.nih.gov/pubmed/8207478 ). It does this by advancing the modulation during the day and slowing it down at night. Mood disorders have been linked to dysfunction in the serotogenic pathway. It may be that the serotogenic pathway dysfunction is actually causing dysfunction in the SCN and this circadian dysfunction is leading to mood issues. This may explain one of the reasons why some people do not fix their mood disorder with SSRIs or L-tryptophan treatment.
GABA also helps to regulate SCN function. Receptors for GABA are found in almost every neuron of the SCN. It was believed that GABA mainly played a role in inhibition of the SCN neurons. However, new information is leading researchers to believe that GABA is excitatory during the day and inhibitory at night (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1402333/#B136 ).
The SCN contains the highest density of melatonin receptors (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC41041/ ). Melatonin is the hormone that responds to darkness and allows us to sleep through the night. Melatonin suppresses SCN activity. Melatonin follows a seasonal cycle. In the winter there is a higher secretion of the hormone than in summer. The rise in seasonal affective disorder may be related to a dysfunctioning circadian clock.
SCN dysfunction is beginning to be looked at as a cause of disease. Studies have linked SCN dysfunction to type 2 diabetes (http://www.ncbi.nlm.nih.gov/pubmed/10587845/ ), high blood pressure, and depression (http://www.ncbi.nlm.nih.gov/pubmed/11448372 ). The SCN plays a role in our energy homeostasis. This is the basis in which dysfunction in the SCN can lead to type 2 diabetes. The dysfunction of the SCN leads to insulin resistance (http://www.ncbi.nlm.nih.gov/pubmed/23274903 ). Leptin may be at the head of all of this.
Leptin can directly modulate the electrical properties of the SCN (http://www.ncbi.nlm.nih.gov/pubmed/19500217 ). This may be the actual avenue in which leptin controls feeding, metabolism, and endocrine behaviors (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC18491/ ). With that said any state of leptin resistance can lead to dysfunction in the SCN and throw off our entire circadian rhythm and lead to disease.
So what does this all mean? To be honest I really do not know. What I do know is maintaining our circadian rhythm is critical to overall health and weight loss. Neurotransmitters require amino acids as precursors, so make sure you are eating enough quality meats, fish, and eggs. Nutrients are required to convert those amino acids into neurotransmitters as well as new tissue so eat lots of veggies. The SCN responds to light so at night time try to sit in dim lighting and not expose yourself to artificial light, especially blue light and sleep in a blacked out room. Eat enough starch to fuel activity. Neurotransmitters also play a role in helping us cope with stress, so manage your stress and let the SCN utilize those neurotransmitters.