risks from overuse of vitamins C and D

I'm not a user of dietary supplements, believing that a diet consisting of a variety of fresh food is likely to provide what is needed, along with some regular exposure to sunshine. Nearly always advice on supplements comes with a recommendation to consult with your physician or medical professional.

I searched for information on Vitamins C and D and zinc, staying  away from sites that were selling them or the services of their clinics.  Here is the main information I found about risks of excessive amounts of C and D.

This site does emphasize that deficiencies in vitamins and minerals is unhealthy and unwise.

https://www.health.harvard.edu/blog/do-vitamin-d-zinc-and-other-supplements-help-prevent-covid-19-or-hasten-healing-2021040522310

Even without convincing evidence, why not take them anyway?

Despite questions about the overall benefit of these supplements, many doctors began prescribing them routinely in the early days of the COVID-19 pandemic. The logic may have been that with so little known about how to best treat this new infection and a long track record of safety for these supplements, why not?

But there are significant hazards to consider. These include side effects, allergic reactions, interactions with other drugs, the cost of unnecessary supplements, and the dangers of taking too much. For example:

• High doses of vitamin C may cause diarrhea or stomach upset. There have also been concerns that high-dose vitamin C supplementation may interfere with blood thinners or cholesterol-lowering medications.
• High doses of vitamin D can cause severe symptoms, such as stomach upsets, kidney injury, and pancreatitis, and may even be life-threatening.

That said, people with nutritional deficiencies should receive supplements. Zinc or vitamin D deficiencies are not rare, and may contribute to poor immune function. Therefore, even without specific evidence linking supplement use with improvement among people with COVID-19, these supplements may be appropriate for people in whom deficiency is suspected or confirmed. For example, a person with little sun exposure and a diet low in dairy products may be likely to have vitamin D deficiency. A simple blood test can confirm or rule out vitamin D or zinc deficiency.

If you do take supplements, it’s safest to follow the daily recommended amounts your body needs unless your doctor advises otherwise (see this information for people 51 and older, and this information on a full range of supplements).