Using national survey data from 2007 to 2010, about 39% of people in the US aged 4 and older, and 49% of children aged 4 to 18, took in less calcium than the estimated average requirement from food and supplements. Blood calcium is tightly controlled by drawing on bone, so long-term low intake mainly shows up as bone loss rather than abnormal blood levels. Low blood calcium (below 8.5 mg/dL) usually comes from medical causes such as low vitamin D or magnesium, parathyroid problems or certain drugs, not from diet alone.
Common symptoms
Most long-term calcium shortfall is silent until a fracture occurs
Bone pain and muscle weakness (osteomalacia)
Fragile bones and higher fracture risk (osteoporosis)
In children: rickets, with bowed legs, delayed growth and soft skull bones
Low blood calcium: muscle cramps and spasms, especially in the hands and face
Tingling around the mouth or in fingertips and toes
Trousseau and Chvostek signs (clinical hypocalcemia indicators)
Seizures (severe low blood calcium)
Heart rhythm disturbances (severe cases)
At-risk groups
Postmenopausal women (estrogen loss accelerates bone resorption)
Older adults (decreased intake plus reduced absorption)
Adolescent girls (peak bone-building years; intake often falls short)
People with vitamin D deficiency (vitamin D required for calcium absorption)
People with lactose intolerance who don't substitute calcium-rich foods
Vegans not consuming fortified foods
People with hypoparathyroidism or kidney disease
People on long-term proton pump inhibitors or corticosteroids
People who've had bariatric surgery
When to see a doctorBone pain, muscle cramps, or a fracture from a minor fall should be checked by a doctor, who may order a bone density scan (DEXA) and blood tests for calcium, vitamin D and parathyroid hormone. For long-term bone health, focus first on dietary calcium, adequate vitamin D and weight-bearing exercise. Calcium supplements at 1,000 mg a day with vitamin D increased kidney stones in the WHI trial and have been linked to possible cardiovascular risk, so food sources are preferred.