Although all types of vinegar products are not the same, let's examine why we should preferably add lemon to our salads rather than vinegar (white, apple cider vinegar, or balsamic):

1. Lemon is a natural product (fruit), while vinegar is a product of chemical fermentation-oxidation.

2. A squeezed lemon can offer 21.6mg of vitamin C, while no form of vinegar (white, red, balsamic, apple cider vinegar) contains vitamin C.

3. The vitamin C and citric acid found in lemon may help us better absorb minerals such as iron and calcium from vegetables that would be more difficult to absorb in the first place, due to the chemical complexes formed with other molecules or ions in the structure of plants.
The basic organic acid (acetic acid) contained in common vinegar also assists in the absorption of iron, but to a lesser extent.

4. Vinegar generally contains a smaller amount of antioxidant polyphenols (21mg per 100g of food) compared to lemon juice (42mg per 100g of food) and their concentration depends on the color of the product. Generally, the whiter the vinegar, the smaller its polyphenol content.

- Ascorbic acid (Vitamin C), citric acid and acetic acid in iron absorption.
https://www.researchgate.net/…/7991048_Enhancers_of…

- Ascorbic acid (Vitamin C) and Calcium absorption.
https://www.ncbi.nlm.nih.gov/pubmed/1020374