Both my husband, aged 76, and I, aged 75, have taken CircO2 for three weeks now. I am beginning to notice a difference in my energy level. I have been trying to exercise more, so I still get tired, but am doing more and more each day (in 95 degree heat, no less!) My husband, however, is loving this product even more than I. He is sleeping 7 hours or more at night at a stretch and is vowing to never be without this supplement. He is very active and seems to be going strong even though he works OUTSIDE in this hot, hot summer. We are taking it twice a day to start and will probably cut back when the weather eases and we have achieved the energy levels we want.