Temperature, Humidity, and Risk of Recurrent Gout Attacks
Temperature, Humidity, and Risk of Recurrent Gout Attacks
Of 632 subjects who had experienced at least 1 recurrent gout attack during the follow-up period, we were able to obtain data on temperature for 626 (99%) subjects and on relative humidity for 624 (99%) subjects. A total of 619 subjects (98%) had temperature or humidity data in both case and control periods; of these subjects, 536 (87%) met the ACR preliminary classification criteria for gout.
The characteristics of the participants are presented in Table 1. The average age was 54 years. Participants were predominantly men (78%) of white race (88%), and more than half had received a college education. Subjects were recruited from 49 states and the District of Columbia. Most gout attacks occurred in the lower extremity (92%), particularly in the first metatarsophalangeal joint, and had features of either maximal pain within 24 hours or redness (89%). Approximately 89% of the gout attacks were treated with colchicine, nonsteroidal antiinflammatory drugs, systemic corticosteroids, intraarticular corticosteroid injections, or a combination of these medications. The median time between the onset of a gout attack and completion of the hazard-period questionnaire was 3 days.
Higher temperatures over the prior 48 hours were associated with higher risks of recurrent gout attacks (Figure 1). The odds ratios were 0.60, 0.75, 0.89, 1.0 (reference group: 50–59°F), 1.18, 1.43, and 1.40, respectively, for each of 7 temperature categories starting from less than 30°F over the prior 48 hours (P for linear trend = 0.01) (Table 2). In contrast, there was a reverse "J-shaped" dose-response relationship between relative humidity and the risk of recurrent gout attacks (Figure 2). Risk of gout attacks appeared to be higher when relative humidity was low. Compared with the reference category (which contained the median humidity level of 60%–74%), both extreme humidity categories tended to be associated with a higher risk of recurrent gout attacks (P for quadratic trend = 0.03) (Table 2 and Figure 2).
(Enlarge Image)
Figure 1.
Depiction of the association between average ambient temperature over the prior 48-hour period and risk of recurrent gout attacks using quadratic spline regression in the whole study sample. Internet-based case-crossover study of gout, United States, 2003–2010. (To convert degrees Fahrenheit to degrees Celsius, subtract 32, multiply by 5, and divide by 9.)
(Enlarge Image)
Figure 2.
Depiction of the association between average relative humidity (defined as the amount of atmospheric moisture (i.e., water vapor) present relative to the amount that would be present if the air were saturated at any given time and temperature (29)) over the prior 48-hour period and risk of recurrent gout attacks using quadratic spline regression in the whole study sample. Internet-based case-crossover study of gout, United States, 2003–2010.
The combined associations of temperature and relative humidity on the risk of gout attacks are presented in Table 3. The risk of recurrent gout attacks was elevated with higher temperature and lower humidity. For example, the odds ratio of recurrent attacks increased by 2-fold when the temperature was above 70°F and the relative humidity was below 60% compared with that when the temperature was between 50–69°F and the relative humidity was between 60%–74%. There was also a suggestion of increased risk of gout attack with the combination of higher temperature and higher humidity; however, the association was smaller than that of the combined effect of higher temperature and lower humidity.
When these sets of analyses were restricted to participants who met ACR gout criteria (n = 536), the results did not change materially. Additionally, the results remained similar when analyses were limited to the first attack occurring during the study period and to attacks affecting the lower extremity.
Results
Of 632 subjects who had experienced at least 1 recurrent gout attack during the follow-up period, we were able to obtain data on temperature for 626 (99%) subjects and on relative humidity for 624 (99%) subjects. A total of 619 subjects (98%) had temperature or humidity data in both case and control periods; of these subjects, 536 (87%) met the ACR preliminary classification criteria for gout.
The characteristics of the participants are presented in Table 1. The average age was 54 years. Participants were predominantly men (78%) of white race (88%), and more than half had received a college education. Subjects were recruited from 49 states and the District of Columbia. Most gout attacks occurred in the lower extremity (92%), particularly in the first metatarsophalangeal joint, and had features of either maximal pain within 24 hours or redness (89%). Approximately 89% of the gout attacks were treated with colchicine, nonsteroidal antiinflammatory drugs, systemic corticosteroids, intraarticular corticosteroid injections, or a combination of these medications. The median time between the onset of a gout attack and completion of the hazard-period questionnaire was 3 days.
Higher temperatures over the prior 48 hours were associated with higher risks of recurrent gout attacks (Figure 1). The odds ratios were 0.60, 0.75, 0.89, 1.0 (reference group: 50–59°F), 1.18, 1.43, and 1.40, respectively, for each of 7 temperature categories starting from less than 30°F over the prior 48 hours (P for linear trend = 0.01) (Table 2). In contrast, there was a reverse "J-shaped" dose-response relationship between relative humidity and the risk of recurrent gout attacks (Figure 2). Risk of gout attacks appeared to be higher when relative humidity was low. Compared with the reference category (which contained the median humidity level of 60%–74%), both extreme humidity categories tended to be associated with a higher risk of recurrent gout attacks (P for quadratic trend = 0.03) (Table 2 and Figure 2).
(Enlarge Image)
Figure 1.
Depiction of the association between average ambient temperature over the prior 48-hour period and risk of recurrent gout attacks using quadratic spline regression in the whole study sample. Internet-based case-crossover study of gout, United States, 2003–2010. (To convert degrees Fahrenheit to degrees Celsius, subtract 32, multiply by 5, and divide by 9.)
(Enlarge Image)
Figure 2.
Depiction of the association between average relative humidity (defined as the amount of atmospheric moisture (i.e., water vapor) present relative to the amount that would be present if the air were saturated at any given time and temperature (29)) over the prior 48-hour period and risk of recurrent gout attacks using quadratic spline regression in the whole study sample. Internet-based case-crossover study of gout, United States, 2003–2010.
The combined associations of temperature and relative humidity on the risk of gout attacks are presented in Table 3. The risk of recurrent gout attacks was elevated with higher temperature and lower humidity. For example, the odds ratio of recurrent attacks increased by 2-fold when the temperature was above 70°F and the relative humidity was below 60% compared with that when the temperature was between 50–69°F and the relative humidity was between 60%–74%. There was also a suggestion of increased risk of gout attack with the combination of higher temperature and higher humidity; however, the association was smaller than that of the combined effect of higher temperature and lower humidity.
When these sets of analyses were restricted to participants who met ACR gout criteria (n = 536), the results did not change materially. Additionally, the results remained similar when analyses were limited to the first attack occurring during the study period and to attacks affecting the lower extremity.
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