National Sleep Foundation

Chapter 7: Sleep-Related Movement Disorders

Prevalence of Sleep-Related Leg Cramps

These cramps can occur at any age, although their prevalence and frequency increases after 50. Up to 60 percent of adults, and 7 percent of children report that they have experienced Sleep-Related Leg Cramps. Approximately 20 percent of these individuals have symptoms severe enough to seek medical treatment.57

References 

57 Cleveland Clinic, Nocturnal Leg Cramps, Cleveland: Cleveland Clinic, 2015. Available online at:  https://my.clevelandclinic.org/health/diseases_conditions/hic_Nocturnal_Leg_Cramps.