Here are some studies about vitamin D and osteomalacia (rickets):
Low Vitamin D Status Has an Adverse Influence on Bone Mass, Bone Turnover, and Muscle Strength in Chinese Adolescent Girls (2009)
Conclusion: In a study of 301 young Chinese girls, those with the higher vitamin D levels demonstrated superior handgrip strength and had higher bone mass.
Effect of Vitamin D Replacement on Musculoskeletal Parameters in School Children: A Randomized Controlled Trial (2006)
Conclusion: For a one-year period 179 girls ages 10-17 were given either a weekly placebo, low dose of vitamin D, or higher dose of vitamin D. After one year the girls given the higher dose of vitamin D showed the biggest increase in lean muscle mass and bone density, especially among the younger girls.
Prevalence of Severe Hypovitaminosis D in Patients With Persistent, Nonspecific Musculoskeletal Pain (2003)
Conclusion: Of 150 patients seeking treatment for chronic musculoskeletal pain, 93% were found to be vitamin D-deficient.
Conclusion: Osteomalacia patients experienced improved physical performance following three months of vitamin D treatment. Another study was performed on 55 vitamin D-deficient veiled Arab women living in Denmark who were experiencing reduced muscle function due to hypovitaminosis D myopathy. They were put on high-dose vitamin D treatment for 6 months and showed improved muscle function after 3 months and 6 months compared to a control group.
Conclusion: 30 cases of infant and childhood nutritional rickets in North Carolina were analyzed. 100% of the patients were dark-skinned, had been breast-fed an average of 12 months, and did not receive vitamin D supplements prior to their rickets diagnoses. Dark-skinned people tend to have disproportionately lower vitamin D levels due to the melanin in their skin blocking UVB solar radiation necessary for vitamin D synthesis. Babies who are breastfed by vitamin D-deficient mothers without receiving vitamin D supplements tend to develop even more severe vitamin D deficiencies than their mothers.
Severe Generalized Bone Pain and Osteoporosis in a Premenopausal Black Female: Effect of Vitamin D Replacement (1998)
Conclusion: A vitamin D-deficient woman with worsening musculoskeletal pains was put through a vitamin D and calcium therapy program. The bone pain was resolved within 4 months along with significantly increased bone density.
Conclusion: Compared to normal women, depressed women tend to have lower bone mineral density. Both depression and lower bone mineral density are symptoms of vitamin D deficiency.
Conclusion: Hip fracture rates for newborns reach their peak January-February and occur least July-August. These rates are in correlation with seasonal vitamin D level changes. Adequate vitamin D is essential for bone health.
Conclusion: In an 18-month-long randomized control trial experiment involving 3,270 elderly women, participants being treated with supplemental calcium and vitamin D suffered 32% fewer nonvertebral fractures compared to a placebo group.
Relation of Fractional 47Ca Retention to Season and Rates of Bone Loss in Healthy Postmenopausal Women (1991)
Conclusion: A study of 58 postmenopausal women over a two-year period found that their calcium retention was higher August-October. This is a time of year when people’s vitamin D levels tend to be highest. The study also found that their calcium retention was lower March-May, after coming out of winter when people’s vitamin D levels tend to be lower. Seasonal changes in calcium retention and bone loss are strongly correlated with seasonal changes in population vitamin D levels.
Conclusion: Women’s bones tend to be stronger at the end of summer compared to the end of winter. This correlates with the well-documented seasonal changes in population vitamin D levels.
Conclusion: It was observed and documented as early as 1942 that people’s calcium absorption rates reached their lowest level right after winter’s end and reached their highest level at the end of summer. It was speculated back then that this had something to do with seasonal fluctuations in the amount and strength of available sunlight and vitamin D, and, indeed, does correlate with more recent research into seasonal changes of vitamin D levels.