The team found that girls who took supplements during the winter had no decrease in vitamin D status during this time and actually improved their bone mineral levels in the femur.
Since the sun is the largest source of vitamin D for most people, individuals who live in areas where winter days are shortest synthesize little or no vitamin D on the skin during those months and have to rely on dietary sources of vitamin D.
Yet although it is well documented that vitamin D decreases the incidence of fractures in the elderly, this is one of the first studies to investigate vitamin D's performance in bone accumulation during adolescence. However bone growth during puberty may be important in preventing osteoporosis and fractures later in life.
From the age of 50, one in three women and one in 12 men will have an osteoporotic fracture, such as those of the hip, wrist or spine.
Speaking this weekend at the second joint meeting of the European Calcified Tissue Society and the International Bone and Mineral Society, lead researcher Dr Heli Viljakainen said: "We believe the current recommendation for adequate vitamin D intake for this age group currently is too low and adolescent girls must receive 10-15 micrograms/day, at least in the northern latitudes."
"To maintain optimal vitamin D status gained during the summer supplementation should begin in autumn to maintain sufficient vitamin D in winter months," she added.
Viljakainen and her colleagues recruited 225 girls aged between 11 and 12 and assigned them to receive a daily dose of 5 micrograms vitamin D3, 10 micrograms of vitamin D3 or a placebo for one year.
They also collected data on pubertal development, height and weight, physical activity and dietary intake of vitamin D and calcium, as well as bone and urine samples. The bone mineral density of the lumbar spine and left femur were measured at the beginning and end of the study with dual x-ray absorptiometry.
For study participants who received 10 micrograms/day, no wintertime decrease in vitamin D status was found and parathyroid hormone concentration, which increases during winter due to low vitamin D status and can negatively affect bone, remained stable throughout the year.
Bone mineral accumulation in the femur increased in study participants receiving 5 micrograms/day by 14.3 per cent, and by 17.2 per cent in the 10 microgram/day group, as compared to the placebo group. Corresponding results were seen in the lumbar spine.
The US Food and Nutrition Board at the Institute of Medicine currently recommends 5 micrograms/day as adequate intake for vitamin D. In Finland and other Nordic countries, the current recommended rate is higher at 7.5 micrograms/day. However, these recommendations do not fluctuate throughout the year.