5. a. You can increase your absorption of calcium by getting adequate amounts of vitamin D.

If you’re not getting adequate vitamin D, the calcium is not going to be absorbed. You can get vitamin D from sunlight, your diet, or supplements. The National Osteoporosis Foundation recommends 400-800 IUs of vitamin D a day and 1,000 mg of calcium a day for premenopausal women or postmenopausal women taking estrogen. Postmenopausal women not taking estrogen and women over 65 need 1,500 mg/day of calcium.