Chel 2008.

Methods	Randomised, double‐blind, placebo‐controlled trial using parallel group design (six intervention groups).
Participants	Country: the Netherlands. Number of participants randomised: 338 (77% women), aged 70 years or over (mean age 84), nursing home residents. Inclusion criteria: nursing home residents aged 70 years or over. Exclusion criteria: going outside in the sunshine more than once a week, the use of vitamin D or calcium supplementation, the use of more than one vitamin D fortified food or drink per day, complete immobilisation and a very poor life expectancy.
Interventions	Participants were randomly assigned to receive: Intervention group 1: vitamin D3 (600 IU) daily (n = 55); Intervention group 2 (control group): matched placebo tablet daily (n = 57); Intervention group 3: vitamin D3 (4200 IU) weekly (n = 54); Intervention group 4 (Control group): matched placebo tablets weekly (n = 58); Intervention group 5: vitamin D3 (18,000 IU) powder monthly (n = 57); Intervention group 6 (Control group): matched placebo powder monthly (n = 57); for a four and a half month period. The treatment period of four and a half months was completed by 276 out of 338 participants. The 276 participants who completed the vitamin D intervention trial were randomly assigned to receive: Intervention group: calcium 800 mg or 1600 mg daily (n = 138); Control group: matched placebo tablet daily (n = 138); for the period of 4 months. The treatment was completed by 269 participants. The first 156 randomised participants received 800 mg calcium carbonate or placebo; the subsequent 120 participants received 1600 mg calcium carbonate or placebo.
Outcomes	The primary outcome was to assess efficacy of different doses and intervals of oral vitamin D3 supplementation with the same total dose. Secondary outcome measure was to assess the additional effect of calcium supplementation following vitamin D supplementation on serum parathyroid hormone and markers of bone turnover.
Stated aim of study	"To investigate, in a Dutch nursing home population, whether there is a difference in efficacy of different doses and intervals of oral vitamin D3 supplementation with the same total dose compared with placebo. A second aim was to assess the additional effect of calcium supplementation following vitamin D supplementation on serum parathyroid hormone and markers of bone turnover."
Notes	"The trial medication was centrally distributed to ensure compliance. Random samples of the returned medication were counted in order to verify compliance." "The compliance assessed within 96 random samples of the returned medication was good. In the daily administration group, all 33 participants were compliant, used at least 80% of the tablets. For weekly administration, 80% of the 35 participants were compliant, used at least 80% of the tablets. For monthly administration, 93% of the 28 participants were compliant, used at least four out of five powders." Solvay Pharmaceuticals supplied the research medication.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The trial is described as randomised but the method of sequence generation was not specified.
Allocation concealment (selection bias)	Unclear risk	The trial was described as randomised but the method used to conceal the allocation was not described, so that intervention allocations may have been foreseen in advance of, or during, enrolment.
Blinding (performance bias and detection bias) All outcomes	Unclear risk	The trial was described as double blind, but the method of blinding was not described so that knowledge of allocation was possible during the trial.
Incomplete outcome data (attrition bias) All outcomes	Low risk	The numbers and reasons for dropouts and withdrawals in all intervention groups were described.
Selective reporting (reporting bias)	Low risk	Pre‐defined, or clinically relevant and reasonably expected outcomes are reported on.
Industry bias	Unclear risk	Solvay Pharmaceuticals supplied the research medication.
Other bias	Low risk	The trial appears to be free of other components that could put it at risk of bias.