Recommended intake for adults, in milligrams per day (recommended calcium allowances based on North American and western European data):
- Adolescents, 10–18 years - 1300 mg / day
- Females, 19 years to menopause - 1000 mg / day
- Females, pregnant women (last trimester) - 1200 mg / day
- Females, lactating women - 1000 mg / day
- Females, postmenopause - 1300 mg / day
- Males, 19–65 years - 1000 mg / day
- Males, 65+ years - 1300 mg / day
The calcium requirement of an adult is generally recognized to be the intake required to maintain calcium balance and therefore skeletal integrity.
Calcium balance is determined by the relationship between calcium intake and calcium absorption and excretion. Relatively small changes in calcium absorption and excretion can neutralize a high intake or compensate for a low one.
A positive calcium balance (net calcium retention) is required throughout growth, particularly during the first 2 years of life and during puberty and adolescence. These age groups therefore constitute populations at risk for calcium deficiency, as do pregnant women (especially in the last trimester), lactating women, postmenopausal women, and, possibly, elderly men.
Vitamin C, or L-ascorbic acid, or ascorbate, is an essential nutrient for humans, a water-soluble vitamin. Humans, unlike most animals, are unable to synthesize vitamin C, so it is an essential dietary component.
- Vitamin C is required for the biosynthesis of collagen (an essential component of connective tissue), L-carnitine, and certain neurotransmitters, it is also involved in protein metabolism.
- Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Vitamin C regenerates vitamin E by reducing vitamin E radicals formed when vitamin E scavenges the oxygen radicals.
- Vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods.
Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg a day. At doses above 1 g a day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine.
Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, connective tissue weakness, and capillary fragility.
Cells accumulate vitamin C. The total body content of vitamin C ranges from 300 mg (at near scurvy) to about 2 g.
- High levels of vitamin C are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and brain.
- Relatively low levels of vitamin C are found in extracellular fluids, such as plasma, red blood cells, and saliva.