33, f, acid reflux disease, does it cause malnutrition or loss of vitamins or does the regular use of antacids cause it?

No, nothing serious: Acid reflux disease, sometimes called, GERD does not cause any nutritional effects. Most antacids used to treat acidity are benign and of minimal consequences. PPIs do have some rare effects on electrolytes like magnesium and Calcium but only after many years of use. This can lead to occasional bone fractures but they are so rare the benefit is much greater than the risk.