Gout attacks do occur more often at night, confirming previous suspicions that date as far back as the 17th century, said the authors of an article published in the February 2, 2015 issue of the journal Arthritis & Rheumatology.
There have been many theories about why people with gout seem to experience more painful attacks at night, ranging from changes in body temperature to sleep apnea. But until this study, no one has found definitive evidence of nocturnal gout exacerbations, the authors wrote.
The study included 724 patients with a confirmed diagnosis of gout who experienced a total of 1,433 attacks over the 9 year study period. The researchers evaluated demographics (sex, age, race, body mass index, education, and household income), as well as information about purine-rich foods consumed before the attack, medications taken for gout, alcohol consumption, and history of sleep apnea.
Study group make-up:
- Predominantly male: 494 subjects (68.2%)
- Median age: 54 years (21-88 years)
- Predominantly white: 642 subjects (88.7%)
- More than half college-educated: 421 subjects (58.2%)
- Median duration of disease: 5 years (1-55 years)
The hours of the day were divided into three 8-hour blocks: midnight to 5:59 AM (block 1), 8 AM to 3:59 PM (block 2), and 4 PM to 11:59 PM (block 3).
During the 1-year follow-up , 733 attacks were reported in block 1, 310 in block 2, and 390 in block 3. This translated to a 2.4 times higher number of attacks during the night and early morning hours vs daytime hours. There did not appear to be any relationships between consumption of alcohol or purine-rich foods within 24 hours before the attack, nor medication use, sex, age, or obesity status of the subjects.
Various hypothesis exist about nocturnal gout attacks. They include:
Body temperature: Daytime body temperature is, for most people, approximately 37.5oC, which drops from 6 pm to approximately 36.4oC Lower temperatures could lead to higher risk of UA crystallization.
Dehydration: Some researchers suspect that overnight relative dehydration could lead to increased risk.
Variation of blood cortisol levels: Blood cortisol levels drop after sleep onset. The authors noted that this could also explain the morning stiffness often felt by people with rheumatoid arthritis.
Sleep apnea: Reports of sleep apnea are not uncommon among men with gout, particularly if they are obese. Sleep apnea and subsequent hypoxia could contribute to generation of purines. “Up to 50% of sleep apnea patients have been found to have hyperuricemia, and therefore, sleep apnea could predispose individuals to gout flares,” they wrote. Patients with sleep apnea could also be at risk for gout flares because of an increased ratio of UA excretion to creatinine excretion.
This study is important because it may have implications for developing effective prophylactic treatments to reduce the risk of gout attacks at night, the authors concluded.
Choi HK, Niu J, Neogi T, et al. Nocturnal Risk of Gout Attacks. Arthritis & Rheumatology. 2015; 67: 555–562. February 2015. doi 10.1002/art.38917