Variation in creatinine production is common. The production of creatinine differs among and within people over time. As examples, individuals with significant variations in dietary intake (e.g., vegetarian diet, creatine supplements) or reduction in muscle mass (e.g., by amputation, malnutrition, muscle wasting) produce different amounts of creatinine than the general population.
There are five key causes of low creatinine:
Low muscle mass
Levels of creatinine are linked with muscle mass or the amount of muscle in the body, which can decrease with age or illness.
Liver problems
Creatinine is made in the liver, and an unhealthy liver that is not working properly will not be able to make the normal amount of creatinine.
Diet
Creatine is mostly found in meat, so those who follow a vegetarian or low-protein diet are likely to have lower levels than people who eat meat.
A prolonged period of not eating or having an illness that suppresses eating can cause low creatinine levels.
Excessive water intake will also lower urine creatinine.
Medications
Diuretics, particularly, lower urine creatinine.
Pregnancy