Feb 26 (Reuters) - R.J. Reynolds Tobacco Co. said it does not add nicotine to its cigarettes, nor does it modify its manufacturing standards to increase nicotine levels over time, as some recent studies suggested.

Responding to recent studies by the Massachusetts Department of Public Health and Harvard University School of Public Health, R.J. Reynolds, an indirect unit of Reynolds American Inc. (RAI.N: Quote, Profile , Research), said it has invited researchers to assess its blending and manufacturing processes. (Reporting by Sayantani Ghosh in Bangalore)