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Melatonin – Cortisol Index

The importance of melatonin and cortisol

Melatonin is a hormone that supports a healthy immune system and is the main hormone involved in synchronizing the daily cycle of light exposure and physical activity in the body (like the body’s internal clock). Melatonin also supports a proper sleep cycle. Cortisol is critical for maintaining energy and supporting a healthy immune system. Cortisol is the hormone that gets you up in the morning and keeps you awake and active most of the day.

Melatonin and cortisol tend to run opposite to each other. Cortisol tends to approach its low point at bedtime or when the sun goes down. Melatonin tends to rise to its peak a few hours after cortisol bottoms out, usually in the evening. Deviations from normal patters of these hormones can have a significant implication for overall health and future risk of chronic disease and even cancer.

Research shows that low melatonin and high cortisol are independently associated with some health conditions. Consequently, the balance between these two hormones is important to overall good health. The melatonin-cortisol index (MCI) is an innovative way of examining the balance between these two vital hormones. The MCI may be used to assess cancer risk and immune function, and may also aid in the assessment of depression, heart disease, osteoporosis and weight management issues.

Sampling Times:


Sampling involves 3 times: waking, noon and bedtime. An individual exposed only to natural lighting will have a very low melatonin level throughout the day (due to light exposure). As the ambient light intensity falls in the evening the melatonin level begins to rise and peak between 2 and 4 am. Exposure to early morning light increases the suppression of melatonin to a low level, but the extent of suppression depends on the timing and intensity of light exposure after waking.


The significance of abnormal cortisol levels is well established in literature and both high and low values have clinical implications. The strength of the relationship between cortisol and melatonin levels emerges on assessment of the diseases and conditions associated with abnormal melatonin cortisol index.

Conditions linked to melatonin-cortisol index:

Disturbances in melatonin and cortisol production have been associated with the following:

Potential Increase of Breast Cancer Risk

Breast cancer research clearly links melatonin levels with breast cancer cell growth. A study by Blask et al. demonstrated that melatonin-rich blood suppressed the growth of human breast cancer. No tumor growth suppression was seen in tumors feeding from melatonin-deficient blood collected from women after short-term exposure to bright at night. Thus, there is a solid link between low late-night melatonin output, and workers with increased night light exposure (seen in shift workers) are at increased risk for breast cancer. Cortisol levels are also tied to breast cancer risk. Breast cancer patients with high average cortisol throughout the day and elevated cortisol at bedtime have earlier mortality, lower natural killer (NK) cells which are part of a strong immune system.

Other Cancers

Circulating levels of melatonin are depressed in a wide variety of cancers including breast, endometrial, prostate, lung, gastric and colon. Studies have show that lower night melatonin levels are associated with larger tumors in patients with prostate cancer. Melatonin in the blood stimulates anti-cancer defenses and exhibits anti-tumor antioxidant activity.

Immune Function

Animal research has shown that inhibition of melatonin synthesis weakens cellular and humoral immunity. Melatonin increase production of interleukin 2 and interleukin 6 (IL-2 and IL6) which indicate immune activity. Melatonin receptors are found in the lymphatic tissue of the body supporting the premise that melatonin has a direct link to immune function. Literature also suggests that low cortisol may lead to overactive early inflammatory immune responses.

Cardiovascular Disease

Low nighttime melatonin has been reported in patients with coronary heart disease and heart failure. Similarly the link between high cortisol and hypertension has been well established.


Research shows that depressed patients have lower levels of melatonin than non-depressed patients. Melatonin supplementation helps correct sleep disorders in depression, although it does not improve clinical symptoms of depression. High levels of cortisol are also associated with depression.


Melatonin has been shown to increase bone mass through its ability to down regulate osteoclastic activity. Osteoclasts are cells that absorb bone reducing bone mass. High levels of cortisol stimulate osteoclastic activity reducing bone mass.

Weight Management

Restoring melatonin to levels of early adulthood may suppress age-related gains in body fat. In addition, high cortisol levels promote deposition of body fat, especially around the mid-section. Therefore, maintaining a melatonin level in the under 40 years range and reducing cortisol levels may be important in weight management.