Vitamin D supplementation to prevent depression and poor physical function in older adults: Study protocol of the D-Vitaal study, a randomized placebo-controlled clinical trial

Table 4 Assessed domains, instruments and their time points in the D-Vitaal study

		Time point
Domain	Instrument	Screening	T0 (baseline)	T1 (6 months)	T2 (12 months)
Primary outcome variables:
Depressive symptoms	CES-D	X	X	X	X
Functional Limitations	LASA-FL	X	X	X	X
Functional Limitations	SF-36 PCS	Partly	X	X	X
Physical performance	SPPB		X	X	X
Secondary outcome variables:
Major depressive disorder	CIDI	X		X	X
Anxiety	BAI		X	X	X
Health-related quality of life	SF-36		X	X	X
Health-related quality of life	EQ-5D		X	X	X
Cognition	Stroop test		X	X	X
Physical performance
Mobility	TUG		X	X	X
Hand grip strength	Dynamometer		X	X	X
Health care costs	TiC-P		X	X	X
Serum 25(OH)D		X		X
Possible covariables:
Demographic information
Age, sex		X
Education level			X
Marital status			X	X	X
Lifestyle
Smoking behaviour			X	X	X
Alcohol consumption			X	X	X
Physical activity	LAPAQ		X	X	X
Blood pressure	Omron device		X	X	X
Anthropometry
BMI	Height, weight		X	X	X
Waist and calf circumference	Tape measure		X	X	X
Chronic diseases	7 majors		X	X	X
Medication and supplement use			X	X	X
Predictors of vitamin D status			X	X	X
Use of counselling			X	X	X

CES-D: Centre of Epidemiological Studies Depression scale; LASA-FL: Longitudinal Aging Study Amsterdam Functional Limitations questionnaire; SF-36 PCS: Short Form 36 Health Survey - Physical Component Summary score; SPPB: Short Physical Performance Battery; CIDI: Composite International Diagnostic Interview; BAI: Beck Anxiety Inventory; EQ-5D: EuroQol 5 Dimensions; TUG: Timed Up-and-Go test; TiC-P: Trimbos and iMTA questionnaire on Costs associated with Psychiatric illness; LAPAQ: Longitudinal Aging Study Amsterdam Physical Activity Questionnaire