How come I cannot increase my dosage of Calcium intake to the RDA of 1000mg? I can tolerate 250mg of calcium supplement in addition to about 300mg to 400mg calcium from diet per day. But I cannot tolerate 500mg of calcium intake from vitamin supplement (in addition to the calcium I get from my diet). I do take food that are rich in calcium. Still my upper limit without negative reaction from total calcium intake (supplement 250mg + diet about 350mg) per day is about 650mg, which still I cannot rich the RDA. Last year December was the first time I tried to increase my calcium supplement intake from 250mg to 500mg. After several days, my heart beat became abnormal, then I had excessive thirst and urination. Finally for several hours, my heart almost burst and I had problem breathing in addition to severe thirst and frequent urination. I knew for sure if the problem did not go away, I would either ended up in coma and had a heart attack. Even I had adverse reaction and really did need emergency care, I did not call 911 because the cost to use an ambulance is at least $1000. I just stayed on my bed for several hours, then my heart contraction was less severe. Still, it took me 2 1/2months to stop taking 250mg of calcium supplements as well as to eliminate foods that are high in Calcium to get my heart beat back to normal. Recently, on around 5/11/2013, this is the third time I tried to increase my Calcium supplement intake from 250mg to 500mg, hoped to reach the RDA of 1000mg/day in addition to dietary intake. But after several days, my heart rate became abnormal and therefore I immediately stop my calcium supplement intake. It has been three weeks now, I still have moderate thirst at night time which cause me unable to sleep. And recently (within this three to four weeks) I do have lots of hair loss which I am not sure if it is related to hypercalcemia. I was born with low birth rate of 3 pounds, then my weight shrunk to 2.5 pound. I am about 5 feet and weigh about 96 pound. I have small bone frame even compare to women about or even shorter than my height. Everyone says my bone is smaller/thinner than normal. So I guess I really don t need that much calcium as the RDA suggests? The only reason I want to increase my Calcium intake is because the RDA says so. Or I will have very high risks to certain cancers and osteoporosis. Also I had minor black out recently (it happened four times since 5/31/2013 to 6/7/2013). I don't know if it is related to hypercalcemia. I used to have very frequent black out several years ago. Once I got up from bed, I would immediately black out or when I bend down and got up. Then it disappeared for a few years and came back about a year ago and then stopped. Since the last black out to the recent black outs was about at least a year. And today is 6/7, my heart rate is getting better, almost back to normal (if I continue to watch/monitor my dietary intake of Calcium, less than 200mg/day). Recently I stopped taking vitamin D supplement for two days. I used to take 600IU/day. But now I am taking 500IU/day. Thanks for your time.