A few people commented on a post last week regarding calcium. I thought that I’d write a little bit more about calcium to clear up a few questions.
The first is calcium in foods. While certain foods such as spinach are a good source of calcium (about 31 mg per raw cup) they may also contain other components (in the case of spinach, oxalic acid) which bind to the calcium and inhibit absorption. Foods that are high in oxalic acid include: sweet potatoes, rhubarb, and beans. Foods that are high in phytic acid include: high fibre foods and grains, beans, nuts, and seeds. Studies have not been able to determine the full extent to which these inhibitors actually affect absorption; however, if calcium is a nutrient that you may not be getting enough of it is worth considering consuming calcium-rich foods in meals separate from these foods. You may have also heard that coffee and tea can lower calcium absorption. They do increase calcium excretion due to the caffeine but the amount is insignificant (about 2-3 mg) so you can continue to drink your lattes to get your calcium if that’s your thing.
The amount of calcium consumed in a sitting can affect absorption. Absorption rates are highest at amounts of 500 mg or less. Thus, taking lower dose supplements spread throughout the day is likely to be of more benefit than taking one large dose a day. The type of calcium supplement you take makes a difference as well. Calcium carbonate (the most common supplemental form of calcium) is 40% calcium and should be taken with meals as stomach acid is necessary for proper absorption. Calcium citrate is more expensive than calcium carbonate, is 21% calcium, but need not be taken with meals for absorption. Other, less common forms of calcium supplements are: calcium phosphate (38% calcium), calcium lactate (13%), and calcium gluconate (9%).
Other factors can increase the absorption of calcium present in foods. For example, a cup of cooked spinach provides about 250 mg of calcium. Consumption of vitamin D also increases calcium absorption. Your age and need for calcium also impacts absorption rates. Calcium absorption is highest in young children and in women during pregnancy as it’s needed for building bone mass. Absorption continues to decrease throughout adulthood; hence higher recommended consumption amounts for women over age 50 and all adults over 70.
As mentioned previously, milk, and fortified milk alternatives, are all good sources of calcium. In addition, here are a few more sources to consider: plain yoghurt (450 mg/cup), Parmesan cheese (390 mg/oz), canned salmon, with bones (210 mg/3 oz), tofu, made with calcium carbonate (140 mg/0.5 cup), kale, cooked (99 mg/cup), dry roasted almonds (85 mg/25 nuts).