Does dietary zinc/copper balance matter?

Question

Cronometer, a tool for tracking micronutrients that is popular with some vegans and vegetarians, provides this nutrient balance indicator which suggests that dietary intake of zinc should be around 10x that of copper. Is this scientifically supported?

On their blog, Cronometer rationalizes showing this nutrient ratio thusly:

It is common practice to recommend a ratio of 8-15 mg of zinc for every 1 mg of copper consumed. However, this ratio seems to be more important when supplementing zinc and copper, compared to meeting needs through diet alone. https://cronometer.com/blog/nutrient-ratios-zinccopper/

Searching for zinc copper ratio with Google yields many websites that make claims about importance of having the correct ratio, but none of these websites appear to be reputable, and none of them link back to scientific studies.

Here is one webpage which paints a particularly dire picture of "the zinc-deficient vegan". However, the author concludes with their belief that veganism is bad for humans and does not explore ways that vegetarians may improve their zinc status, which gives the impression that the author has quite a chip on their shoulder. The author also recommends HMTA (hair mineral tissue analysis) which is popular among holistic nutritionists but not well regarded among other medical professionals.

It appears that Weston A. Price foundation was the first to publish materials raising concern about Zinc:Copper imbalance first with their magazine in 2007, then with a blog post from 2008.

If dietary balance of zinc and copper does matter, and if 10:1 is a desirable ratio, then this should be a concern for vegetarians and vegans especially because virtually all* foods of plant origin (except nutritional yeast) have a Zn:Cu ratio of less than 10:1.

If dietary balance of zinc and copper does not matter and it's enough to just ensure sufficient intake of each trace mineral, then vegans using Cronometer may be unnecessarily concerned or misled, and perhaps this page can serve as a useful resource to alleviate concern.

Answer 1

I asked a Registered Dietitian in Canada and received this answer:

Zinc/copper balance is only a concern when taking zinc or copper mineral supplements. Just focus on getting enough zinc from whole foods and you'll be fine.

This is similar to what I found in the Cronometer blog post about nutrient ratios:

Nonetheless, it is common practice to recommend a ratio of 8-15 mg of zinc for every 1 mg of copper consumed. However, this ratio seems to be more important when supplementing zinc and copper, compared to meeting needs through diet alone. Osredkar J, Sustar N. Copper and zinc, biological role and significant of copper/zinc imbalance. J Clinic Toxicol. 2011; S3:001.

And if high doses of zinc are supplemented, copper deficiency is known to occur (although elevated copper does not seem to interfere with zinc absorption, provided zinc intake is adequate).

And finally, the Tolerable Upper Intake Level for copper (TUL = 10.0 mg) is 11 times higher than the recommended dietary allowance (RDA = 0.9 mg). This means that we have considerable flexibility in our diet without worrying about copper toxicity. A strict vegetarian diet provides zinc in a ratio of about 5:1 with copper, so meeting the zinc RDA of 12 mg would provide, on average, about 2.4 mg of copper, well within safe limits.

I made a diagram to help explain this. The healthy range of zinc and copper intake is shown (according to published RDA and TUL values) in the white space. The suggested 8:1 intake is shown as a blue diagonal. I've plotted a vegan diet as the range between 4:1 and 6:1 since many plant foods are in this range. Note in particular that around a typical diet of 2000 kcal/day, there is a huge safety margin before copper toxicity occurs. However, obtaining sufficient zinc may be a challenge so one should either consume additional energy, or include some zinc-rich foods like oatmeal and nutritional yeast (examples shown in purple).

TL;DR Vegans should not be concerned about zinc/copper balance.