Due to little outdoor activity and low dietary intake of vitamin D (VD), Bangladeshi low-income women are at risk for osteoporosis at an early age. The present study assessed the effect of VD, Ca and multiple micronutrient supplementation on VD and bone status in Bangladeshi young female garment factory workers. This placebo-controlled 1-year intervention randomly assigned 200 apparently healthy subjects (aged 16–36 years) to four groups: VD group, daily 10 μg VD; VD and Ca (VD-Ca) group, daily 10 μg VD+600 mg Ca; multiple micronutrient and Ca (MMN-Ca) group, 10 μg VD and other micronutrients+600 mg Ca; a placebo group. Serum 25-hydroxyvitamin D (S-25OHD), intact parathyroid hormone (S-iPTH), Ca, phosphate and alkaline phosphatase were measured. Bone mineral density and bone mineral content were measured by dual-energy X-ray absorptiometry. All measurements were made at baseline and at 12 months. Significantly (P < 0·001) higher S-25OHD concentrations were observed in the supplemented groups than in the placebo group after the intervention. Supplementation had an effect (P < 0·001) on S-iPTH in the VD-Ca and MMN-Ca groups compared with the placebo group. Bone mineral augmentation increased at the femur in the supplemented groups. Supplementation with VD-Ca should be recommended as a strategic option to reduce the risk of osteomalacia and osteoporosis in these subjects. MMN-Ca may have analogous positive health implications with additional non-skeletal benefits.