If you don't get enough vitamin D through sunlight or food sources, you might need vitamin D supplements. See vitamin D recommendations.
Taken in appropriate doses, vitamin D supplementation is generally considered safe. The National Academy of Medicine (USA) recommends an average daily intake of 400–800 IU, or 10–20 micrograms. The safe upper limit is 4,000 IU. Make sure not to take more than that unless recommended by your doctor.
Note: Many seniors have low vitamin D levels. This is because they tend to stay indoors or avoid sunshine, and because in older adults the skin produces less vitamin D when exposed to the sun as compared to younger people.
IOF recommends that adults aged over 60 years take a vitamin D supplement of 800 to 1000 IU/day to benefit bone health.