Scientists randomly assigned 25,871 women aged 55 or older and men aged 50 or older to take a placebo or vitamin D (2,000 IU) every day.

After five years, there was no difference in fracture rates between the vitamin D takers and the placebo takers.

Only 13 percent of the participants entered the study with “inadequate” blood levels (lower than 20 nanograms per milliliter), and only 2 percent had “deficient” levels (less than 12 ng/mL). What’s more, roughly 40 percent of the participants were also taking vitamin D (up to 800 IU a day) on their own.

What to do

Don’t expect extra vitamin D to prevent bone fractures. To reach adequate blood levels of vitamin D, aim for the RDA: 

• 600 IU a day up to age 70, or
• 800 IU a day if you’re over 70 

Foods like dairy milk and some plant milks and cereals are fortified with 100 to 200 IU per serving, but most foods have little or none, so you may need a supplement.