Calcium, Magnesium and Phosphorus
1. What are the best methods of
assessment for calcium, magnesium and phosphorus?
•
Phosphorus can be assessed by monitoring serum concentration and urinary
excretion; when dietary intake of phosphorus increases the serum level
increases as well; also, when urinary excretion increases this can indicate
high dietary intake, high PTH and acidosis. We also have to keep in mind that when
urinary excretion decreases this means that there is an effect on calcitriol,
alkalosis, estrogen, thyroid and growth hormones.
•
For Magnesium, serum levels are tightly controlled, and due to this, it is not
a good marker for the status of magnesium in the body. Therefore, the best way
to assess magnesium is through urine excretion before and after magnesium is
administered into the body intravenously. When the body is deficient in
magnesium, it will hold onto it opposed to excreting it through the urine. When
an individual is deficient in magnesium less than 80% of the magnesium is
secreted.
•
Like magnesium, serum calcium is tightly regulated making this a poor marker
for the status of calcium. Instead serum calcium reflects alterations of
calcium metabolism, in this we need to keep in mind that albumin levels must be
considered, as calcium binds to albumin to be transported through the blood.
The best way to assess calcium status is to observe bone mass. DEXA is used to
measure bone mineral contents this is the best method because it is accurate
and repeatable.
6. What are the best foods for
calcium, magnesium and phosphorus – and which foods/nutrients inhibit
absorption?
•
Milk and dairy are the best sources of calcium. Other sources include tofu and
sardines with the bone. However, orange juice fortified with calcium is also a
good source because the acidity in the orange juice will help the body absorb
more of the calcium. Leafy greens, including spinach, turnip greens and
collards are also good non-dairy sources of calcium. Some nutrients that help
to enhance calcium absorption include: vitamin D, sugars and sugar alcohol, and
protein. On the other hand, nutrients/substances that inhibit calcium
absorption include: fiber, phytic acid, oxalic acid, unabsorbed fatty acid and
excessive zinc and magnesium.
•
Magnesium is in a wide variety of foods, food processing and preparation may
reduce the magnesium content of the food. High sources of magnesium are sesame
seeds, halibut, almonds and cashews, other sources that are not as high
include: spinach, black beans, and brown rice. Nutrients/substances that help
enhance the absorption of magnesium include: vitamin D, protein, carbohydrates
and fructose. There are some interactions with magnesium and they include
calcium, phosphorus, and potassium. Nutrients that inhibit the absorption of
magnesium are phytic acid, fiber and excess unabsorbed fatty acids.
•
Phosphorus is the second most abundant mineral, and like magnesium, it is in a
wide variety of foods. Some high sourced foods include: beef liver, and milk,
other sources include: chicken, oysters and peanut butter. It has been studied
and determined that animal products are a better source of phosphorus than
plant sources. One nutrient that can help with the absorption of phosphorus is
vitamin D, and nutrients that can inhibit the absorption are phytic acid, and
excessive intakes of magnesium, calcium and aluminum [1].
The NIH suggested that
the two forms of calcium in supplements and carbonate and citrate. Calcium carbonate
is more commonly available and is both inexpensive and convenient due to its
dependence on stomach acid for absorption, it explains that calcium carbonate
is absorbed most efficiently when taken with food, whereas calcium citrate is
absorbed equally well when taken with or without food. This will explained
comments on orange juice and other fortified juices with high acidity and their
function on absorption of calcium in the body [2].
Some absorbed
calcium is eliminated from the body in urine, feces and sweet. Per the NIH
protein intake with high sodium increases urinary calcium excretion; recent
research suggested that high protein intake also increases intestinal calcium
absorption therefore the conclusion is that protein with help with calcium
absorption with moderate sodium intake. Caffeine intake is another way of
losing calcium from the body for example one cup of regular brewed coffee
causes a loss of 2-3 mg of calcium. Phosphorus intake, will have some effect on
calcium excretion however, is minimal. Several observational
studies suggest that consumption of carbonated soft drinks with high levels of
phosphate is associated with reduced bone mass and increased fracture risk.
However, the effect is probably due to replacing milk with soda rather than the
phosphorus itself [2].
1.
Gropper S, Smith J, Carr T., Advanced Nutrition and Human Metabolism. 7th
ed. Boston, MA: Cengage Learning; 2018
2. NIH. Calcium. Website. Last Updated
November 17, 2016. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
Accessed on November 5, 2017.
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