- Oxalate in chocolate binds with Calcium to make it not bioavailable
- Sugar in chocolate increases Calcium excretion
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Chocolate: Does it impair calcium absorption?
A friend told me that chocolate impairs absorption of calcium. Is this true?
Answer, from Katherine Zeratsky, R.D., L.D.
Chocolate contains oxalate — a naturally occurring compound in cocoa beans — which can inhibit the absorption of calcium. Calcium binds to oxalate in your intestines, limiting its absorption into your bloodstream. People with oxalate kidney stones, which could occur when there is too much oxalate in the urine, should limit the amount of oxalate in their diets.
The jury is still out, however, on whether chocolate causes problems for healthy people who eat calcium-rich diets. A 2008 study suggests there might be reason for concern. The study found that elderly women who ate one or more servings of chocolate a day had lower bone density and strength than did women who ate fewer servings of chocolate. Researchers believe this may be due to oxalate inhibiting calcium absorption — but it could also be due to the chocolate's sugar content, which may increase calcium excretion. In addition, chocolate also contains flavonoids, which are thought to be beneficial to health. Further research is needed to fully determine the role chocolate plays in calcium balance and bone strength.
In the meantime, if you get the daily recommended amounts of calcium and vitamin D from food or supplements, and practice weight-bearing exercise, eating chocolate in moderation is unlikely to adversely affect your bone health.
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Am J Clin Nutr. 2008 Jan;87(1):175-80.
Hodgson JM, Devine A, Burke V, Dick IM, Prince RL.
Royal Perth Hospital Unit, the University of Western Australia School of Medicine and Pharmacology, Perth, Australia. jonathan.hodgson at uwa.edu.au
BACKGROUND: Nutrition is important for the development and maintenance of bone structure and for the prevention of osteoporosis and fracture. The relation of chocolate intake with bone has yet to be investigated.
OBJECTIVE: We investigated the relation of chocolate consumption with measurements of whole-body and regional bone density and strength.
DESIGN: Randomly selected women aged 70-85 y (n=1460) were recruited from the general population to a randomized controlled trial of calcium supplementation and fracture risk. We present here a cross-sectional analysis of 1001 of these women. Bone density and strength were measured with the use of dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and quantitative ultrasonography. Frequency of chocolate intake was assessed with the use of a questionnaire and condensed into 3 categories: <1 time/wk, 1-6 times/wk, >or=1 time/d.
RESULTS: Higher frequency of chocolate consumption was linearly related to lower bone density and strength (P<0.05). Daily (>or=1 times/d) consumption of chocolate, in comparison to <1 time/wk, was associated with a 3.1% lower whole-body bone density; with similarly lower bone density of the total hip, femoral neck, tibia, and heel; and with lower bone strength in the tibia and the heel (P<0.05, for all). Adjustment for covariates did not influence interpretation of the results.
CONCLUSIONS: Older women who consume chocolate daily had lower bone density and strength. Additional cross-sectional and longitudinal studies are needed to confirm these observations. Confirmation of these findings could have important implications for prevention of osteoporotic fracture.
PMID: 18175753 PDF is online
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Chocolate supplies oxalic acid, which reacts with the calcium in the milk producing calcium oxalate, thus preventing the calcium from being absorbed in the intestine. However, it is present in small enough amounts that the effect on calcium absorption is negligible.
As chocolate contains relatively small amounts of oxalate, it is unclear to what extent chocolate consumption affects healthy people who eat calcium-rich diets. In a 2008 study, participants who consumed one or more servings of chocolate on a daily basis had lower bone density and strength than those participants who ate a serving of chocolate six times a week or less.
Researchers believe this may be due to oxalate inhibiting calcium absorption — but it could also be due to the chocolate's sugar content, which may increase calcium excretion. It is clear, however, that consuming foods high in oxalate — and in turn their effect on calcium absorption — is a more significant concern for people with oxalate kidney stones, which occur when there is too much oxalate in the urine. These people, especially, should reduce their oxalate intake and increase their calcium intake.
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- example more oxalate in Spinach, beets, etc.
About 50 milligrams of Oxalate per 100 grams of chocolate.
7 gram chew piece has 500 mg of Calcium
Compute that a 7 milligram piece of chocolate has 50*(7/100) = 3.5 milligrams of Oxalate
If we wildly assume that 1 milligram of Oxalate ties up 1 milligram of Calcium (probably right within a factor of 3)
then a piece of chocolate calcium chew would have 500 - 7 = 493 milligrams of Calcium - not much loss