Why women should not perform Religious rituals in Menstrual Days | The 4th Way | The4way.net

The reason is the fact that performing or attending religious ceremonies and rituals, or entering temples during menstruation over a long period of time may have an adverse effect on the health of the menstruating woman

The energy present at a properly consecrated temple, or the energy generated in a properly performed religious ritual, will facilitate spiritual upliftment and calmness of the mind in those who participate, by causing the Apana vayu to move upwards. This upward movement will interfere with the downward movement of Apana vayu that is facilitating menstruation. This interference will result in imbalance of the Prakriti Doshas, which in-turn will affect the health of the menstruating woman over a long duration.
Thus, menstruating women have been advised not to take part in any religious activity, including visiting temples, so as to fulfil the dual purpose of: facilitating maintenance of the spiritual atmosphere at the temples and during the religious ceremonies, without any disturbance to its energy and spiritual environment; and protecting the menstruating woman from any adverse effects on her health due to interference with her physiological functioning of Doshas.
At this point, it is important to highlight that the practice of most of these menstrual restrictions have been given up by the current generation, though many of them still practice few of the restrictions, especially those related to religious practices. According to a study by Dr. Jasmine Gujarathi, Dr. Dilip Jani and Dr. ARV Murthy [2], which interviewed girls from urban and rural background, noted that out of 798 girls interviewed, only 14.16% followed restriction on cooking. 

Similarly, restriction on touching others, sleeping on same bed, and on applying turmeric and kajal were followed by 10.90%, 5.89%, and just 2.38% of girls respectively. Adherence to menstrual restrictions was highest with respect to religious practices like not participating in religious activity (41.60%) and not visiting temple (47.62%). Only 25 girls (3.13%) said that they did not follow any restriction