Reading large data from Excel into MATLAB

I have about 30 .xlsx sheets, with n X 5 columns of data. Each sheet has n = 400,000 rows of data (approx.). I am currently reading in the sheets, and using vertcat() to merge the data (i.e. 30n rows x 5 columns).

My script is something like this:

for k=1:numel(d);
data{k}=xlsread(fullfile(folder,d(k).name));
end

Is there a better and faster way to merge the data?