Many people don’t get recommended amounts of calcium from the foods they eat, including:
Boys aged 9 to 13 years, 
Girls aged 9 to 18 years, 
Women older than 50 years, 
Men older than 70 years. 
When total intakes from both food and supplements are considered, many people—particularly adolescent girls—still fall short of getting enough calcium, while some older women likely get more than the upper limit. See our Health Professional Fact Sheet on Calcium for more details.
Certain groups of people are more likely than others to have trouble getting enough calcium:
Postmenopausal women because they experience greater bone loss and do not absorb calcium as well. Sufficient calcium intake from food, and supplements if needed, can slow the rate of bone loss. 
Women of childbearing age whose menstrual periods stop (amenorrhea) because they exercise heavily, eat too little, or both. They need sufficient calcium to cope with the resulting decreased calcium absorption, increased calcium losses in the urine, and slowdown in the formation of new bone. 
People with lactose intolerance cannot digest this natural sugar found in milk and experience symptoms like bloating, gas, and diarrhea when they drink more than small amounts at a time. They usually can eat other calcium-rich dairy products that are low in lactose, such as yogurt and many cheeses, and drink lactose-reduced or lactose-free milk. 
Vegans (vegetarians who eat no animal products) and ovo-vegetarians (vegetarians who eat eggs but no dairy products), because they avoid the dairy products that are a major source of calcium in other people’s diets. 
Many factors can affect the amount of calcium absorbed from the digestive tract, including:
Age. Efficiency of calcium absorption decreases as people age. Recommended calcium intakes are higher for people over age 70. 
Vitamin D intake. This vitamin, present in some foods and produced in the body when skin is exposed to sunlight, increases calcium absorption. 
Other components in food. Both oxalic acid (in some vegetables and beans) and phytic acid (in whole grains) can reduce calcium absorption. People who eat a variety of foods don’t have to consider these factors. They are accounted for in the calcium recommended intakes, which take absorption into account. 
Many factors can also affect how much calcium the body eliminates in urine, feces, and sweat. These include consumption of alcohol- and caffeine-containing beverages as well as intake of other nutrients (protein, sodium, potassium, and phosphorus). In most people, these factors have little effect on calcium status.