A high intake of zinc interferes with magnesium...
In a carefully controlled study, people taking a supplement containing
45 milligrams of zinc (for a total of 53 milligrams from supplements
and diet) had decreased magnesium balance.
The study, published in the May 2004 issue of the European Journal
of Clinical Nutrition, looked at 25 women with an average age
of 65 years
The women lived in a metabolic ward for six months so everything
they ate, drank and excreted was measured.
Moderately high intake of zinc increased the loss of magnesium
in both urine and feces. It also unfavorably altered two markers
of bone formation in the women.
People taking zinc supplements or using zinc lozenges to treat
cold symptoms can get up to 150 milligrams of zinc. These amounts
can interfere with copper metabolism and depress HDL-cholesterol
and immune functions.
Because they tend to eat more, physically active people consume
zinc in amounts exceeding the recommended daily amount (12 milligrams
for women and 15 milligrams for men).
However, certain groups (endurance athletes, for example) often
consume a lot of carbohydrate. This can displace other foods —
such as red meat — that contain high levels of zinc.
Unfortunately, it's difficult to establish whether you're getting
enough zinc. Although measuring levels in the blood is one way to
diagnose a severe zinc deficiency, it's not sensitive enough to
establish a moderate zinc deficiency.
Good sources of zinc include sirloin steak (4.4 milligrams per
3 ounces), lamb chop (4 milligrams per 3 ounces), and turkey (2.6
milligrams per 3 ounces). Six large oysters provide over 20 milligrams
of zinc.
If you don't eat these foods on a regular basis, then a vitamin
and mineral supplement can reduce your risk of a zinc deficiency.
Reference
Nielsen, F.H., & Milne, D.B. (2004). A moderately high intake
compared to a low intake of zinc depresses magnesium balance and
alters indices of bone turnover in postmenopausal women. European
Journal of Clinical Nutrition, 58, 703-710
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