This mess started towards the end of the winter, a long period of low sunlight and presumably lower vit D levels. What's the rate of VDI in 75 year olds in gene

This mess started towards the end of the winter, a long period of low sunlight and presumably lower vit D levels. What's the rate of VDI in 75 year olds in general towards the end of winter? I can't find any numbers, but I suspect it'll be close to 100% in any non-warm climate.