1. What is zinc?
Zinc is an essential trace mineral that plays many roles in the body. It
is a component of over 100 enzymes and plays key roles in reproductive function,
immune function, and the transport of Vitamin A. Some of the best sources
of zinc are crab, beef, turkey, and ham.
2. What application does zinc have?
The utility and need for zinc supplements in athletes is still controversial.
It is known that mild zinc deficiency is common in both the general public
(6) and athletes specifically (1), but the impact this has on athletic performance
is unknown (2). However, there are quite a few reasons to believe that correcting
mild zinc deficiency could improve athletic performance, especially in males.
First, zinc deficiency is associated with lower testosterone levels (3) and
higher estrogen levels (4). Secondly, zinc depletion has negative effects
on immune function that can be corrected with supplementation (5). Finally,
zinc deficiency may independently lead to lower leptin levels (7). The impact
mild zinc deficiency has on the development of insulin resistance in humans
has yet to be established.
3. How should I take zinc?
The inorganic forms of zinc found in multivitamins are usually not absorbed
very well (8), which is another reason for additional supplementation. Zinc
is most bioavailable when it is binded to a ligand/chelator (such as EDTA),
amino acid (such as histidine) or organic acid (such as citrate) (6). Zinc
methionine is an exception, with studies showing it to have low bioavailability
equal to that of the inorganic forms chloride and proprionate, and it is
hypothesized that the bond is not strong enough to survive the upper GI tract
(6, 9). Zinc picolinate is one of the most bioavailable forms (10), but one
of the best ways to increase zinc absorption in any form is to eat it with
a large amount of meat or whey protein (casein may inhibit absorption), and
this may prevent the inhibitory effect phytates normally have on zinc absorption
(6). Although calcium, iron, and copper can all interfere with zinc absorption,
studies in human adults confirm that this only happens when the ratio between
the two elements is very uneven (6).
The recommendations for daily intake vary between 12-15 mg per day for men
or 8-12 mg for women, and the UL (tolerable upper intake) is 40 mg. A low
dose zinc supplement should be all that is needed to prevent a deficiency,
although up to 30 mg is commonly taken with relative safety. The most important
concern with zinc supplementation is the possibility of copper deficiency
(11), and if you choose to use high doses of zinc (40 mg+ per day) the general
recommendation is an extra 100 mcg of copper for each 10 mg of zinc.
Some of the best zinc supplements are
Optimum ZMA and
Now Zinc Picolinate (which I
recommend taking every other day).
If you have any questions or comments regarding this article, please email
dvdtlsn@bulknutrition.com.
No part of this article may be reproduced in any form without the permission of David Tolson or Mike McCandless. 
