Zinc deficiency causes proteins to lose their shape. Such proteins stop working and clump together, forming the toxic plaque behind Alzheimer's. Find out how much zinc you need to keep your brain healthy. Check out the best foods to keep zinc in balance.
Scientists at UW-Madison have made a discovery that, if replicated in humans, suggests a shortage of zinc may contribute to diseases like Alzheimer's and Parkinson's, which have been linked to defective proteins clumping together in the brain.
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Zinc and the Brain
With proteins, shape is everything. The correct shape allows some proteins to ferry atoms or molecules about a cell, others to provide essential cellular scaffolding or identify invading bacteria for attack. When proteins lose their shape due to high temperature or chemical damage, they stop working and can clump together — a hallmark of Parkinson's and Alzheimer's.
Photo: Colin MacDiarmid and David Eide/Journal of Biological Chemistry
The UW researchers have discovered another stress that decreases protein stability and causes clumping: a shortage of zinc, an essential metal nutrient.
Zinc ions play a key role in creating and holding proteins in the correct shape. In a study just published in the online Journal of Biological Chemistry, Colin MacDiarmid and David Eide show that the gene Tsa1 creates "protein chaperones" that prevent clumping of proteins in cells with a zinc shortage. By holding proteins in solution, Tsa1 prevents damage that can otherwise lead to cell death in the brain.
How much zinc do I need?
The amount of zinc you need each day depends on your age. Average daily recommended amounts for different ages are listed below in milligrams (mg):| Life Stage | Recommended Amount |
|---|---|
| Birth to 6 months | 2 mg |
| Infants 7–12 months | 3 mg |
| Children 1–3 years | 3 mg |
| Children 4–8 years | 5 mg |
| Children 9–13 years | 8 mg |
| Teens 14–18 years (boys) | 11 mg |
| Teens 14–18 years (girls) | 9 mg |
| Adults (men) | 11 mg |
| Adults (women) | 8 mg |
| Pregnant teens | 12 mg |
| Pregnant women | 11 mg |
| Breastfeeding teens | 13 mg |
| Breastfeeding women | 12 mg |
What foods provide zinc?
Zinc is found in a wide variety of foods. You can get recommended amounts of zinc by eating a variety of foods including the following:- Oysters, which are the best source of zinc.
- Red meat, poultry, seafood such as crab and lobsters, and fortified breakfast cereals, which are also good sources of zinc.
- Beans, nuts, whole grains, and dairy products, which provide some zinc.
How the Research was Done
For simplicity, the researchers studied the system in yeast — a single-celled fungus. Yeast can adapt to both shortages and excesses of zinc, says MacDiarmid, an associate scientist. "Zinc is an essential nutrient but if there's too much, it's toxic. The issue for the cell is to find enough zinc to grow and support all its functions, while at the same time not accumulating so much that it kills the cell."Cells that are low in zinc also produce proteins that counter the resulting stress, including one called Tsa1.
The researchers already knew that Tsa1 could reduce the level of harmful oxidants in cells that are short of zinc. Tsa1, MacDiarmid says, "is really a two-part protein. It can get rid of dangerous reactive oxygen species that damage proteins, but it also has this totally distinct chaperone function that protects proteins from aggregating. We found that the chaperone function was the more important of the two."
"In yeast, if a cell is deficient in zinc, the proteins can mis-fold, and Tsa1 is needed to keep the proteins intact so they can function," says Eide, a professor of nutritional science. "If you don't have zinc, and you don't have Tsa1, the proteins will glom together into big aggregations that are either toxic by themselves, or toxic because the proteins are not doing what they are supposed to do. Either way, you end up killing the cell."
While the medical implications remain to be explored, there are clear similarities between yeast and human cells. "Zinc is needed by all cells, all organisms, it's not just for steel roofs, nails and trashcans," Eide says. "The global extent of zinc deficiency is debated, but diets that are high in whole grains and low in meat could lead to deficiency."
If low zinc supply has the same effect on human cells as on yeast, zinc deficiency might contribute to human diseases that are associated with a build-up of "junked" proteins, such as Parkinson's and Alzheimer's. Eide says a similar protective system to Tsa1 also exists in animals, and the research group plans to move ahead by studying that system in human cell culture.
Am I getting enough zinc?
Most people in the United States get enough zinc from the foods they eat.However, certain groups of people are more likely than others to have trouble getting enough zinc:
- People who have had gastrointestinal surgery, such as weight loss surgery, or who have digestive disorders, such as ulcerative colitis or Crohn's disease. These conditions can both decrease the amount of zinc that the body absorbs and increase the amount lost in the urine.
- Vegetarians because they do not eat meat, which is a good source of zinc. Also, the beans and grains they typically eat have compounds that keep zinc from being fully absorbed by the body. For this reason, vegetarians might need to eat as much as 50% more zinc than the recommended amounts.
- Older infants who are breastfed because breast milk does not have enough zinc for infants over 6 months of age. Older infants who do not take formula should be given foods that have zinc such as pureed meats. Formula-fed infants get enough zinc from infant formula.
- Alcoholics because alcoholic beverages decrease the amount of zinc that the body absorbs and increase the amount lost in the urine. Also, many alcoholics eat a limited amount and variety of food, so they may not get enough zinc.
- People with sickle cell disease because they might need more zinc.
Do I Get Too Much Zinc?
Yes, you can get too much. Signs of too much zinc include nausea, vomiting, loss of appetite, stomach cramps, diarrhea, and headaches. When people take too much zinc for a long time, they sometimes have problems such as low copper levels, lower immunity, and low levels of HDL cholesterol (the "good" cholesterol).The safe upper limits for zinc are listed below. These levels do not apply to people who are taking zinc for medical reasons under the care of a doctor:
| Life Stage | Upper Safe Limit |
|---|---|
| Birth to 6 months | 4 mg |
| Infants 7–12 months | 5 mg |
| Children 1–3 years | 7 mg |
| Children 4–8 years | 12 mg |
| Children 9–13 years | 23 mg |
| Teens 14–18 years | 34 mg |
| Adults | 40 mg |
Where can I find out more about zinc?
- For general information on zinc:
- For more information on food sources of zinc:
- For more advice on buying dietary supplements:
- For information on the government's food guidance system:
SOURCES:
- National Institutes of Health - Office of Dietary Supplements
- Univesrity of Wisconsin-Madison
- Manchester Life Sciences
The research on humans that the article suggests should be done has already been done. Supplementary zinc has been shown to be helpful for Alzheimer's patients.
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