Many people have experienced sudden lower extremity cramps at night while getting ready for bed or during sleep. In some people, the pain is enough to wake the person up, and the pain can be relieved by pulling hard on the cramped muscle. Since a significant number of patients are elderly, they go to the doctor and are often told that they are deficient in calcium and asked to take calcium supplements. Many people are confused, I usually take calcium supplements, why do I still have cramps? There is a line in the New Year’s Eve drama “The Greatest Showman”: “We Chinese have been taking calcium supplements en masse”. Indeed, through various media campaigns over the years, everyone believes that Chinese people are deficient in calcium, so various calcium supplements have been created, and many people have already taken calcium supplements. But there is a logical problem here, since it is a calcium deficiency, why is it that only the lower limbs cramp? In fact, this is a widespread sleep disorder called nocturnal cramps (nocturnalleg cramps/night cramps), the specific cause is unknown, medical also known as idiopathic night leg cramps, from children to adults have the onset, the overall incidence of children 7.3%, from the age of 8 years onwards, the peak at the age of 17 years, each typical attack lasts about 2 minutes. The incidence increases with age, and about 1/3 of people over 60 years of age have similar episodes. Lower extremity spasms are present in 33%-50% of pregnant women and worsen with the course of pregnancy. Nocturnal leg spasms mainly affect the leg, foot or thigh muscles and occur at night in the majority of patients (73%), with 20% having episodes during the day and night and 7% having episodes only during the day. The average attack lasts 9 minutes, with the longest duration of symptoms in the thigh. 40% of patients have more than three attacks a week, and 6% have daily attacks. The spasms can occur at any time throughout sleep including rapid eye movement sleep (REM) and may originate from abnormal spontaneous firing of motor neurons in the anterior peduncle of the spinal cord, abnormal motor nerve terminal excitation, hyperactivity of motor units in the presence of spinal cord de-inhibition, or enhanced muscle contraction through neuronal cross-activation. Local ischemia and metabolic waste accumulation can cause pain. In 2005, the American Academy of Sleep Medicine proposed diagnostic criteria for sleep-related leg cramps: Painful sensations in the leg or foot associated with sudden muscle stiffness or tension, including intense muscle contractions. Painful muscle contractions of the leg or foot occur during sleep and can occur during waking or sleeping states. Pain can be relieved and muscles can be relaxed by vigorous stretching of the affected muscles. Sleep-related leg spasms cannot be explained by other known sleep disorders, medical or neurological abnormalities, drug use or substance abuse. Other causes of nocturnal leg spasms include restlesslegs syndrome (RLS), periodic limb movements, vascular claudication, peripheral neuropathy, dystonia, and electrolyte disturbances, whose symptoms are easily confused with nocturnal leg spasms. The twitching caused by low calcium is a tonic spasm of bilateral limbs, hand and foot twitching, with the upper limbs showing wrist flexion, finger extension, metacarpophalangeal flexion, thumb inversion near the palm and opposite to the little finger, forming the so-called “midwife’s hand”, and the lower limbs showing “ballet foot”. This shows that most nocturnal lower limb twitches in the elderly are not caused by low calcium. For nocturnal cramps, the internationally recommended treatment is Quinine, and clinically, many patients with combined venous insufficiency of the lower extremity can be relieved with Diosmin tablets or horse chestnut seed extract.