The ideal way to provide building blocks for metabolism and repair is to provide the most basic building blocks possible. Sometimes, due to many different factors, the body needs a product that doesn't require multiple steps to do it's job.
Vitamin D is an example. We have very complex and effective ways to synthesize Vitamin D (which is a hormone, not a vitamin) via skin exposed to the sun.
If you live in a northern climate, have dark skin, obesity, or are elderly, the system may not be able to keep up and you benefit from supplementation.
When you supplement, you need to know the correct amount to take, and what to take with the Vitamin D (K2 and Vitamin A) and some fat; taking the supplement incorrectly can result in too much or too little Vitamin D.
When taking any supplement, it is a good idea to know why you are taking it, and if are you taking the safest most effective substance to support your body as it maintains your health.
Help your body take care of you by drinking enough water; if you have a persistent cough, an accessible, economical treatment is being well hydrated.
Think of the cilia in your respiratory tract as hairs that protect your lungs. They work best when well hydrated- your body uses the water you drink to hydrate essential parts, including the cilia.
There are other things that can help, but reaching for water first, before things get severe can be a good idea.
Our bodies have great abilities to adapt to too much or too little water; because of this, we can be complacent and not notice when improving the quality or having a glass of water instead of a different beverage can improve how we feel. Filtered water in a glass or stainless water bottle is healthier than a plastic bottle.
If you are feeling hungry, listless or tired, have a big glass of water and notice if you feel better, there's a good chance it will help.