source("http://192.38.117.59/~linearpredictors/datafiles/readVitaminD.R")

## calculate the histogram without plotting it
h <-  hist(irlwomen$vitd, plot = FALSE)

## frequency is changed to percent
h$counts <- h$counts/length(irlwomen$vitd)*100 
plot(h,
     xlab = "Vitamin D",
     ylab = "Percent",
     main = ""
     )    

## adding a box around the plot
box()