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Low-iodine soil does not mean every New Zealander needs an iodine supplement. Most people should first look at reliable food sources: commercially made bread, milk products, eggs and seafood. Pregnancy and breastfeeding are different: Health New Zealand recommends a registered iodine-only tablet providing 150 micrograms daily alongside food sources. Confirm pregnancy supplements with your midwife, doctor or nurse practitioner.
Do not start iron just because you feel tired. Girls and women have a higher risk of low iron because of menstrual blood loss, and requirements rise in pregnancy. But fatigue, hair shedding, headaches and poor exercise tolerance have many causes. Health New Zealand recommends blood testing and investigation of the cause; if iron is low, a clinician can choose a dose, form and duration and check whether it worked.
Neither magnesium glycinate nor magnesium oxide is universally best. NIH's evidence review says oxide is generally less bioavailable than several more soluble forms. Glycinate may be easier for some people to tolerate, yet direct high-quality evidence that it is always better absorbed or better for sleep is limited. Compare elemental magnesium per daily dose, your reason for taking it, gut response, medicines and price.
New Zealand's low-selenium soils do not prove that you are deficient. Medsafe reports that animal-feed practices and imported foods such as wheat and legumes help most New Zealanders reach around recommended intake. New Zealand dietary supplements must not recommend more than 150 micrograms of selenium per adult daily dose, and selenium has a relatively narrow margin between adequacy and excess.
Zinc deficiency can lower testosterone, but extra zinc has not been shown to reliably “boost” testosterone in zinc-replete people. A 2023 systematic review found that baseline zinc/testosterone status, dose, form and duration changed results; only eight of its 38 included studies were clinical. If you have symptoms of low testosterone, use a clinician-led assessment; a zinc product cannot diagnose the cause, and one hormone result needs timing and clinical context.