documentclass{article}

usepackage{booktabs}
usepackage{dcolumn}

newcolumntype{d}{D{.}{.}{5.5}}
newcolumntype{C}{>{centering}p}

begin{document}

begin{table}[htp]
caption{}
centering
begin{center}
    begin{tabular}{p{1.25in}ddd}
    toprule
    multicolumn{1}{C{1in}}{shortstack{Group}} & multicolumn{1}{C{0.75in}}{shortstack{Weight\(g)}} &    multicolumn{1}{C{1in}}{shortstack{Glucose\(mg/l)}} & multicolumn{1}{C{2in}} {shortstack{Glycosylated protein\(nmol/mg protein)}}\
    midrule
    Control & 544.5 & 908.0 & 17.8\
    Diabetic & 331.2{$^{***}$} & 5736.0{$^{***}$} & 32.10{$^{***}$}\
    Diabetic+GT & 343.9{$^{***}$} & 4037.0{$^{***}daggerdagger$ } &   24.87{$^{***}$}\
    bottomrule
    end{tabular}
end{center}
label{tbl:results}\
end{table}

end{document}