Study Population
NHANES (National Health and Nutrition Examination Surveys) is a series of large, multistage probability surveys designed to be representative of the US civilian, noninstitutionalized population that is conducted by the National Center for Health Statistics (NCHS) and Centers for Disease Control and Prevention. [16] 16 16 16 Detailed descriptions of the survey design and data collection procedures are available elsewhere. [16] 16 16 16 The data are collected via an in-home interview and a visit to a mobile examination center. All participants provided written informed consent and the research ethics boards of the NCHS approved all protocols.
We used data from the 2005–2014 NHANES (including 5 cycles: 2005–2006, 2007–2008, 2009–2010, 2011–2012, and 2013–2014), and a total 14 708 US adult participants ≥ 20 years old met the following inclusion criteria were used in the study: 1) data available on age, sex, race, body mass index (BMI), recreational physical activity, education attainment, and poverty income ratio; 2) the participants responded to the questions on pesticide exposure and depression symptoms.
Measures
Exercise information in a typical week (yes/no) was self-reported during an interview. Moderate and vigorous recreational physical activity, where moderate recreational physical activity is defined as that activities cause a small increase in breathing or heart rate (such as brisk walking, bicycling, swimming, or volleyball for at least 10 minutes continuously); and vigorous recreational physical activity is defined as activities that causes large increases in breathing or heart rate like running or basketball for at least 10 minutes continuously (like running or basketball for at least 10 minutes continuously).
Household pesticide exposure was defined as those who responded to “In the past 7 days, were any chemical products used in home to control fleas, roaches, ants, termites, or other insects?”
Depression symptoms was assessed using the Patient Health Questionnaire (PHQ-9), which is a 9-item depression symptoms screening instrument that asks participants to choose 1 of 4 responses about the frequency of depressive during the previous 2 weeks.[17] Those scoring ≥ 10 were considered as having moderate, moderately severe, or severe depression symptoms.
Antidepressant use was defined as taking at least one prescribed antidepressant medication in the past 30 days. We identified antidepressants using the Lexicon Plus® therapeutic classification (first-level category “Psychotherapeutic Agents”, second level category “Antidepressants”), which included selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, phenylpiperazine, and miscellaneous antidepressants.[18]
For psychological counseling, we defined counseling and various types of therapy as treatment with a mental health professional, which was measured by the survey question, “During the past 12 months, have you seen or talked to a mental health professional such as a psychologist, psychiatrist, psychiatric nurse, or clinical social worker about your health?”
We defined depression symptoms as PHQ-9 total scores ≥ 10, or taking at least one prescribed antidepressant medication in the past 30 days, or receiving psychological counseling treatment.
Weight and height were measured by trained technicians in mobile examination centers who used standardized procedures. Race was based on proxy- or self-report and was categorized as non-Hispanic white, non-Hispanic black, Mexican-American, or other categories. The poverty income ratio is the ratio of a family's income to the US Census Bureau's poverty threshold, which is adjusted for family size and is updated annually for inflation. The poverty income ratio was used as the indicator of socioeconomic status in the analyses. Participants were categorized as never smokers (individuals who have smoked < 100 cigarettes in life), former smokers (having smoked > 100 cigarettes in life but do not currently smoke), and current smokers.
Statistical Analysis
All variables were checked for normality of distribution, and appropriate transformations were applied when necessary. Continuous variables are presented as mean ± SD, whereas categorical variables are presented as cases (n). Logistic regression was used to calculate the odds for the association of pesticide exposure with depression symptoms, and the NHANES sampling weights and complex survey design were considered in the analysis. Univariate analyses were performed in Model 1. Model 2 adjusted for age, sex, and race; Model 3 more adjusted for BMI, recreational physically inactive, marital status, education attainment, and poverty income ratio. In addition, the interactions between pesticide exposure and recreational physical activity. The NHANES does not provide details on antidepressant use and psychological counseling, but the individuals seeking psychological counseling might suffer from other mental illnesses rather than depression, and antidepressants were prescribed for reasons other than depression, so we performed a sensitivity analysis by excluding the participants with antidepressant medication or receiving psychological counseling treatment (1608 participants). In addition, we performed another sensitivity analysis using the PHQ-9 score as a continuous variable. All data analyses were performed using Stata software version 12.1 (STATA Corp., TX, US). A two-sided P < 0.05 was considered statistically significant.