Introduction: The purpose of this research was to study differences between men and women in vitamin D3 levels and between vitamin D3 levels and muscle strength. I hypothesized that there would be no significant difference between vitamin D3 and gender. I also hypothesized that people with more vitamin D3 levels would have greater muscle strength compared to people with low vitamin D levels (Rathmacher, 2015). This is part of a larger NIH study. Methods: Blood serum was drawn from 54 men and 40 women to measure Vitamin D3 levels. After obtaining the results I separated the participants into the top 50th percentile and the lower 50th percentile based on vitamin D3 levels. Muscle strength was measured using a Biodex where the participant sat on the machine and flexed their right leg to 180 degrees with as much force as possible while the machine provided resistance. Results: A T-test revealed no differences between men and women in vitamin D3 levels. In addition there was no difference between the upper 50th percentile and the lower 50th percentile of vitamin D3 levels on muscular strength (p>.05).