Klodian Dhana explains how to build a for loop in R:

I used linear mixed effect model and therefore I loaded the

`lme4`

library. The loop should work with other regression analysis (i.e. linear regression), if you modify it according to your regression model. If you don’t know which part to modify, leave a comment below and I will try to help.As other loops, this call variables of interest one by one and for each of them extract and store the betas, standard error and p value. Remember, this code is specific for linear mixed effect models.

Read the whole thing. It’s good to keep in mind, though, that set-based R operations tend to perform best, so save looping for cases in which you can’t build a set-based function.