It's late at night. The only sound is the low hum of the air conditioner working hard to keep the heat and humidity at bay, and for some reason you cannot sleep. You've worked out during the day and you're absolutely exhausted. No matter — the Sandman refuses to visit.

If you were to consult a traditional Chinese medical (TCM) practitioner about your predicament, they would almost certainly point to your liver.

The function of the liver in traditional Chinese medicine is to regulate the qi, or life force, flowing through the body. In mainstream medicine, the liver is the organ that performs a number of essential biological functions.

TCM practitioner Samuel To Ching-san is a graduate of the University of Hong Kong's School of Chinese Medicine and he has a PhD in acupuncture from Guangzhou University of Chinese Medicine. He has been practising TCM in Hong Kong for more than 13 years.

Sleepless nights or disrupted sleep could be attributed to a condition that can be translated as 'liver fire', he says.

"When there is too much qi, it leads to heat. So when someone's yin (cool, nighttime energy) and yang (warm, daytime energy) are unbalanced, where there is too much yang that leads to the qi overheating the liver, it eventually becomes liver fire," To says.

Apart from sleeplessness, other symptoms include teeth grinding, frustration, a volatile temper and dry mouth and eyes. In extreme cases, it may also lead to depression.

"Sleep is absolutely essential to proper liver function," To adds. "Insomnia is a common symptom of the liver because when your body rests at night, it's what we call in Chinese medicine a transition from yang to yin.

"The liver is most active from 1am to 3am and is the organ that regulates the qi transition. The liver is like a filter for the entire body, converting the 'yang' qi of the day to 'yin' qi at night, hence creating a balance. If that filter is dirty or blocked, the yang will overflow and you wake up."

This TCM theory loosely aligns with Western medicine.

A 2020 review of sleep disorder in patients with chronic liver disease in the Journal of Thoracic Disease notes: "Sleep disturbance is a common feature of chronic liver disease (CLD) with impact on health-related quality of life; 60 to 80 per cent of patients with CLD report subjective poor sleep; frequent presentations of sleep disturbance include insomnia, reduced sleep efficiency, increased sleep latency, reduced time in rapid eye movement sleep, restless leg syndrome and excessive daytime sleepiness."

Why is liver fire-induced insomnia particularly prominent in the summer months? To says: "Heat is all around you in summer, and your liver has to filter all the heat you have absorbed during the day, too."

According to TCM's holistic approach, the largest contributory factor to imbalances in the liver are day-to-day choices in lifestyle and diet.

"Fried or spicy food, coffee, alcohol and staying up late, all contribute to liver heat," says To. "The liver is at its optimum performance between 1am and 3am so it's best to be in bed by 11pm and make sure the body is at rest for the liver to do its job."

TCM practitioners prescribe herbs to target liver health — and overcome insomnia — such as Chinese thorowax root, white peony root, Baikal skullcap root, adhesive rehmannia root tuber, capillary wormwood (a herb) and Siberian Solomon's seal rhizome.

An acupuncturist can also work on relevant pressure points to help stimulate the healing of liver fire.

Let food be your medicine. Some healing soups based on TCM ingredients are readily available at popular Hong Kong Chinese restaurants. The Royal Garden Chinese Restaurant in the basement of the Royal Garden Hotel in Tsim Sha Tsui offers double-boiled teal (duck) with cordyceps flower soup on its menu.

The JW Marriott Hotel Hong Kong's Man Ho restaurant offers double-boiled sea cucumber soup with American ginseng, dendrobium (orchid) and chicken, and double-boiled fish maw soup with conch, cordyceps flower and Silkie chicken.

The active TCM ingredients include American ginseng, dendrobium and cordyceps flower.

"We know that these ingredients help reduce heat and dispel dampness in TCM," says chef Jayson Tang of JW Marriott Hotel Hong Kong.

"The liver helps detoxify the body, and if there are too many toxins in the body then heat will build up, much like how a dirty air conditioner filter will affect how well it functions."

For a good night's sleep, try these mild and simple TCM home remedies.

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This article was first published in South China Morning Post.