Assessment of potential risk and confounding factors

Questions modified from the National FINRISK Studies conducted by the National Public Health Institute were used to assess information on self-reported physician-diagnosed conditions, prescribed medications and other treatments, likewise the use of alternative treatments (Table 4 and Appendix 2). These questions - while not validated - have been extensively used (Vartiainen et al. 1998, Laatikainen et al. 2003, Peltonen et al. 2008).

Comorbidity indicators were formulated for conditions deemed common or previously identified or hypothesised as risk factors of LUTS (Appendix 3). Medication use was based on self-reported medication lists and classified into 27 groups using the Anatomical

Lifestyle factors, including body mass index (BMI), smoking, coffee and alcohol consumption were assessed by questionnaire (Table 4 and Appendix 2). Information on sociodemographic factors (marital status, education, employment, not urbanity) was also assessed by questionnaire (Appendix 2). Information on urbanity, parity (no information on delivery mode) and postpartum period (six weeks to one year after delivery; based on delivery dates) was derived from the Finnish Population Register Centre. Information on menstrual history in past year, MHT, hysterectomy and surgery for SUI (no detail on surgical procedures) was assessed by questionnaire. Women were classified as premenopausal, postmenopausal, hysterectomised, or MHT users (Table 5).

The questionnaire also included a modified version of the Basic Nordic Sleep Questionnaire (Partinen & Gislason 1995) to assess sleep disorders, such as snoring. We used 11 items of the original 21-item questionnaire. The Basic Nordic Sleep Questionnaire uses a five-point scale (with a basic scale of response options such as: 1, “never or less than once per month”;

2, “less than once per week”; 3, “on 1-2 nights per week”; 4, “on 3-5 nights per week”; and 5,

“every night or almost every night”). We used snoring information here based on responses to Basic Nordic Sleep Questionnaire (Table 4 and Appendix 5), which referred to the past two weeks.

Information on physician-diagnosed conditions, medications, specific symptoms, and lifestyle factors was available each for 97%-100% of men and 95%-100% of women. Only the question on alcohol consumption (which was not significantly associated with nocturia) had relatively low response (86% of men, 76% of women). Information on age, socio-demographic and female reproductive/gynaecological factors was available for at least 99% of both sexes.

Table 4. Terms and definitions used regarding potential risk and confounding factors of nocturia in the FINNO Study, Finland, 2003-2004.

Term Defining Questions Response Categorisation

Physician-diagnosed conditions

“Have you ever been diagnosed by a physician with any of the

following conditions?” with numerous response options (Appendix 3). (No) Yes Regular use of

prescribed medication

Regular use of medication was based on self-reported medication lists assessing drug “names, dosages, and frequency of usage (not at all;

“when needed” or “course way”; regularly) (Appendix 4).

No, “When needed” or

“Course way” users Regular users

Lifestyle factors

Alcohol

“How many units of alcohol do you typically drink per week?”

unit of alcohol corresponds bottle of beer (33 cl), glass of wine (12 cl), or restaurant portion of spirit (4 cl)

Units per week

Coffee “How many cups of coffee do you typically drink per day?” Cups per day

Body mass index “How tall are you?” and “How much do you weigh?” were used to calculate body mass index (BMI).

BMI <25 (reference^a)

BMI 25-30 (overweight)

BMI ≥30 (obesity)

Sociodemographic factors

Marital status “What is your current marital status?” Married/Living together, Widowed,

Divorced/Separated, Never married

Education “Which of the following describes your education?” Basic level, Vocational school, College, University

Employment “In the last three months, have you been mainly?” Student, Employed,

Unemployed, Retired

Urbanity Based on data from the Finnish Population Register Centre Small community (less than 50,000 inhabitants), Large community (at least 50,000 inhabitants) Specific symptoms^b

Snoring “How often do you snore while sleeping (ask other people if you are not sure)?” (Partinen & Gislason 1995)^c

Never or less than once per month; Less than once per week; or On

1-2 nights per week

On 3-5 nights per week;

or Every night or almost every night

Stress urinary incontinence

“Do you experience leakage of urine when physically active (e.g.

coughing, sneezing, lifting)?” (Schou et al. 1993) Never or Rarely Often or Always Urinary urgency

(overactive bladder)

“Do you experience an imperative (strong) urge to urinate?” (Schou et

al. 1993)^d Never or Rarely Often or Always

Female reproductive/gynaecological factors

Parity Based on data from the Finnish Population Register Centre Number of delivered children

Postpartum period Based on delivery date data from the Finnish Population Register Centre

Defined as more than 6 weeks but not more than 1 year after delivery

Menopausal status (Classification in Table 5)

“Did you have periods during the last 12 months?” No Yes

“Have you had a hysterectomy?” No Yes

“Do you use hormone therapy for menopausal symptoms?” No Yes

“If you answered yes, do you use vaginal, oral or transdermal?” (No) Yes Surgery for stress

urinary incontinence “Have you had surgery for stress urinary incontinence?” No Yes

a Only 0.3% of male and 3% of female respondents were underweight (BMI <18.5). The prevalence of nocturia was similar in underweight and normal-weight women by either nocturia criterion (≥1 void/night or ≥2 voids/night). Hence, we used non-overweight (BMI <25) persons as the reference group.

b These specific symptoms have been shown to be risk factors for nocturia (Samuelsson et al. 1997, Weiss et al. 1998, Kinn & Harlid 2003).

c We also used another snoring question for a small minority of subjects (for 1% of men and 6% of women of final study population in the Study VI; for subjects who did not provide answer to this but provided answer to another snoring question); details in Appendix 5.

Table 5. Classification of women by menopausal status in the FINNO Study, Finland, 2003-2004.

Characteristic Definition

Premenopausal Non-hysterectomised women without MHT who menstruated during the previous year and non-hysterectomised women under 40 years old

Postmenopausal Non-hysterectomised women without MHT who did not menstruate during last year (and at least 40 years old)

Women with MHT^a Non-hysterectomised women with MHT (and at least 40 years old)

Hysterectomised Women who reported prior hysterectomy

a Menopausal hormone therapy (MHT) included women who reported current use of vaginal or systemic MHT. The prevalence of nocturia was similar between women reporting using vaginal or systemic MHT (age-standardised 15.9% of vaginal and 15.5% of systemic MHT users, p=0.51). Hence, we combined these.