Vitamin D and Calcium: Without It, Absorption Falls Short

What Vitamin D Does

Vitamin D promotes active calcium absorption in the intestines, helps regulate blood calcium levels, and plays a role in bone mineralization. If vitamin D levels are insufficient, actual calcium absorption drops noticeably even when calcium intake meets targets — over time, this can affect bone density. Even a diet that looks ideal on paper for calcium can end up being largely wasted effort without enough vitamin D.

Vitamin D Sources for Vegetarians

• Sunlight: Skin synthesizes vitamin D on its own when exposed to UVB rays. About 15 to 30 minutes a day of sun on bare arms or face is usually enough, though the exact amount of time needed varies with season, latitude, and skin tone.
• Fortified foods: Vitamin D–fortified plant milks and some breakfast cereals.
• Mushrooms: Mushrooms treated with UV light have significantly higher vitamin D content — check the label when buying.
• Supplements: Vegetarians can choose vitamin D2, or vitamin D3 sourced from lichen.

When You May Need to Supplement

Winters with limited sunlight, long-term indoor work, and reduced skin synthesis efficiency in older adults are all situations with a higher risk of vitamin D insufficiency. It's best to check your vitamin D levels through a blood test and supplement under medical guidance if needed, rather than guessing. Don't raise the dose significantly on your own, either — too much vitamin D carries its own health risks.