Zinc is an essential element that should be kept in body within normal limits.
Being essential means that human body can’t synthesize it; rather it should be adequately obtained from diet and/or dietary supplements.
Zinc is one of the elements required for thyroid hormone synthesis, which also include selenium and copper [i].
Moreover, zinc is crucially required for keeping a normal metabolism of thyroid hormones, in addition to maintaining a normal resting metabolic rate (RMR) [ii].
How does zinc affect the thyroid?
Zinc is required to help the thyroid gland work properly. The same time, thyroid hormones are required to ensure absorbing zinc.
Several clinical studies were conducted to reveal the relationship between zinc and the thyroid, as follows:
- In a study of 62 patients, the ones who had zinc deficiency were noted to also have low levels of both the thyroid hormone named triiodothyronine (T3), and the useable amount of this hormone, which is known as free triiodothyronine (TFI) [iii].
- According to a study of hypothyroid patients with and Down syndrome, supplementation with zinc could significantly improve the thyroid functions, increasing the levels of thyroid stimulating hormone (TSH) [iv].
- Another study showed that zinc supplementation normalized the levels of triiodothyronine (T3), serum free T3 and TRH-induced TSH reaction [v].
- According to 2 studies, including 10 sedentary volunteers, and other 10 wrestlers, zinc consumption could prevent the decrease in thyroid hormones, including TT3, TT4, FT3, as well as testosterone, which occur after exercise [vi], [vii].
- According to a recent study of 2013, zinc supplementation helped treat the alopecia associated with hypothyroidism [viii].
- Another recent study of obese patients with hypothyroidism showed that zinc consumption could improve the thyroid function, increasing both mean serum FT3 and mean serum FT4[[ix]].
- According to a study of 2 females, zinc consumption helped improve zinc deficiency, and had a positive effect on the levels of thyroid hormones, in addition to improving the normal resting metabolic rate [1].
Other benefits
Zinc influences not only thyroid related issues, but also plays major roles in other functions and disorders as well. For example:
- Functioning of 2 hundreds of enzymes
- DNA and protein synthesis
Zinc is involved in the synthesis of both DNA and protein. The process of protein synthesis includes many growth factors and steroid receptors, such as thymulin-hormone, which is dependent on zinc, and is involved in maturating some cells responsible for immunity [x].
- Improving immunity
Mild zinc deficiency may negatively affect body immunity. According to a 1998-research article, zinc could affect the balance between both cell-mediated immunity and humoral immunity [[xi]].
- Achieving a normal body growth
Adequate zinc intake helps ensure normal growth, extending from improving cell division [3], pregnancy and up to adulthood [xii], [xiii], [xiv].
How much zinc do people need?
People need to ensure getting sufficient amounts of zinc on daily basis; otherwise they are much likely to many issues.
That’s why the Food and Nutrition Board established values that show how much zinc is needed daily for each person, as follows:
- The adequate intake for infants up to 6 months is 2mg/daily; while those ranging from 7-12 months are recommended to take 3mg/day.
- 3mg of zinc daily is recommended for children ranging from 1-3 years; while those ranging from 4-8 years are recommended to take 5mg of zinc/daily.
- The recommended zinc amounts differ, according to both age and gender, as follows:
- The males and females ranging from 9-13 years are recommended to take 8mg of zinc/day.
- The males aged 19 years or more are recommended to take 11mg of zinc/day.
- The females ranging from 14-18 years are recommended to take 9mg of zinc/day; while those aged 19 years or older are recommended to take 8mg of zinc daily.
- The recommended adequate intake of zinc also differs in pregnancy and breastfeeding, as follows:
- Pregnant women who are 18 years old or younger are recommended to take 12mg of zinc daily.
- Pregnant women who are 19 years old or older are recommended to take 11mg of zinc daily.
- Breast-feeding women aged 18 years or younger are recommended to take 13mg of zinc daily.
- Breast-feeding women aged 19 years or older are recommended to only take 12mg of zinc daily.
Don’t take too much zinc
While everyone needs to get sufficient amounts of zinc; the same time, it is advised to avoid taking too much zinc.
As zinc is a vital element, it should be taken wisely.
That’s why the Food and Nutrition Board established the Upper Levels (UL) allowed of zinc, in order to avoid the issues that are likely to result from taking too much zinc.
- The upper level (UL) for infants up to 6 months is 4mg/daily; while the UL for those ranging from 7-12 months is 5mg of zinc per day.
- 7mg of zinc daily is recommended for children ranging from 1-3 years; while those ranging from 4-8 years are recommended to take 12mg of zinc/daily.
- The males and females ranging from 9-13 years can take zinc as much as 23mg/ day.
- The males and females aged 14-18 years can take up to 34mg of zinc per day.
- Both males and females who are aged 19 years or older are recommended to take up to 40mg of zinc per day.
- Pregnant and breast-feeding women who are 18 years or younger can safely administer up to 34mg of zinc daily.
- Pregnant and breast-feeding women who are 19 years or older can safely take up to 40mg of zinc/day.
The best sources for adequate zinc intake
Zinc can be obtained from 3 sources, including dietary supplements, animal and plant-based foods. Thyroid supplements, such as those featured in Thyroid Advisor, often contain Zinc in addition to Iodine, L-tyrosine, Ashwagandha, and other nutrients.
It is worth mentioning that flesh sources are more recommended, as the zinc they contained in them can be absorbed more easily, compared to that obtained from plant-based sources [1].
According to the fact sheet provided by the National Institute of Health (NIH), what makes the flesh sources more recommended is that many plant-based sources of zinc contain another substance named phytates, which inhibit zinc absorption [xv].
- Animal-based foods containing zinc
- Oysters
- Red meat and Poultry
- Certain types of seafood, such as crab and lobster
- Dairy products
- Plant-based foods rich in zinc
- Whole grains
- Cereals
- Beans
- Nuts
- Legumes
Dietary supplements Vs. natural sources… The best choice is?
Some people compare dietary supplements to natural sources, mistakenly thinking that one choice is better than the other. Actually, both dietary supplements and natural sources should be taken with each other.
The importance of considering dietary supplements is to ensure getting sufficient amounts of zinc daily; not suddenly finding out that you are zinc-deficient.
More importantly, some people are much likely to zinc deficiency. For example, those who tend not to consume various foods, and those struggling with improper digestion and other stomach-related issues, such as irritable bowel syndrome that can negatively affect zinc absorption.
References:
[i] Ambooken Betsy, et al. Zinc Deficiency Associated with Hypothyroidism: An Overlooked Cause of Severe Alopecia. Int J Trichology. 2013 Jan-Mar; 5(1): 40–42.doi: 10.4103/0974-7753.114714[ii] Maxwell C., et al. Effect of zinc supplementation on thyroid hormone function. A case study of two college females. Ann Nutr Metab. 2007;51(2):188-94. Epub 2007 May 30.
[iii] Morley JE, et al. The interrelationship of thyroid hormones with vitamin A and zinc nutritional status in patients with chronic hepatic and gastrointestinal disorders. Am J Clin Nutr. 1981 Aug;34(8):1489-95.
[iv] Bucci I., et al. Zinc sulfate supplementation improves thyroid function in hypozincemic Down children. Biol Trace Elem Res. 1999 Mar;67(3):257-68.
[v] Nishiyama S., et al. Zinc supplementation alters thyroid hormone metabolism in disabled patients with zinc deficiency. J Am Coll Nutr. 1994 Feb;13(1):62-7.
[vi] Kilic M. Effect of fatiguing bicycle exercise on thyroid hormone and testosterone levels in sedentary males supplemented with oral zinc. Neuro Endocrinol Lett. 2007 Oct;28(5):681-5.
[vii] Kilic M., et al. The effect of exhaustion exercise on thyroid hormones and testosterone levels of elite athletes receiving oral zinc. Neuro Endocrinol Lett. 2006 Feb-Apr;27(1-2):247-52.
[viii] Betsy A, Binitha M, Sarita S. Zinc deficiency associated with hypothyroidism: an overlooked cause of severe alopecia. Int J Trichology. 2013 Jan;5(1):40-2. doi: 10.4103/0974-7753.114714.
[ix] Mahmoodianfard S., et al. Effects of Zinc and Selenium Supplementation on Thyroid Function in Overweight and Obese Hypothyroid Female Patients: A Randomized Double-Blind Controlled Trial. J Am Coll Nutr. 2015;34(5):391-9. doi: 10.1080/07315724.2014.926161. Epub 2015 Mar 11.
[x] Prasad AS. Zinc: an overview. Nutrition. 1995 Jan-Feb;11(1 Suppl):93-9.
[xi] Solomons NW. Mild human zinc deficiency produces an imbalance between cell-mediated and humoral immunity. Nutr Rev. 1998 Jan;56(1 Pt 1):27-8.[xii] Simmer K, Thompson RP. Zinc in the fetus and newborn. Acta Paediatr Scand Suppl 1985;319:158-63.
[xiii] Fabris N, Mocchegiani E. Zinc, human diseases and aging. Aging (Milano) 1995;7:77-93.
[xiv] Maret W, Sandstead HH. Zinc requirements and the risks and benefits of zinc supplementation. J Trace Elem Med Biol 2006;20:3-18.
[xv] Office of Dietary Supplements. Zinc. Fact Sheet for Health Professionals. National Institute of Health. Updated: February 11, 2016.