ConsumerLab.com is reporting on an observational study among nearly 10,000 adults (average age 46) in the U.S. who were followed for about 10 years that found that those with high blood levels of vitamin C (about 60 mcmol/L or 1.06 mg/dL or greater) had a 33% greater risk of all-cause mortality and 60% greater risk of cardiovascular disease mortality compared to those with lower levels.
This blood level of vitamin C is at the higher end of what is considered adequate (48 to 70 mcmol/L) and is close to saturated levels. Also, ConsumerLab points out other concerns have been raised:
ConsumerLab writes, “Vitamin C is safe when taken in moderate amounts but be aware that too much vitamin C can cause diarrhea and other gastric disturbances, such as heartburn.”
They add, “Keep in mind that unless you are taking a buffered form of vitamin C (such as calcium ascorbate or sodium ascorbate), vitamin C is acidic. To reduce gastric side effects, divide the dose over the course of a day and take it with meals.”
The Tolerable Upper Intake Level (UL) (i.e., the maximum daily amount likely to be safe for the vast majority of healthy people) for vitamin C in adults is 2,000 milligrams — based on total intake from foods, beverages, and supplements.
The upper level for tolerable intake is 400 mg/day for children ages 1 to 3, 650 mg/day for children ages 4 to 8, 1,200 mg/day for children ages 9 to 13, and 1,800 mg/day for teens ages 14 to 18 ages.
Individuals are generally advised not to exceed these levels unless under medical supervision.
To answer the question, “How much vitamin C should I take?” ConsumerLab advises:
To be sure you’re getting the daily requirement of vitamin C, a supplement providing roughly 50 mg to 100 mg of vitamin C is sufficient for most adults and is quite safe. Be aware, however, that taking more than 500 mg of vitamin C per day on a regular basis (which will saturate your blood with vitamin C) may increase your risk of developing cataracts, and taking more than 1,000 mg per day may also increase your risk of kidney stones. In fact, while adequate levels of vitamin C in the body are associated with reduced risk of death, this appears to reverse at higher levels. Diarrhea can result from a single dose of more than 2,000 mg for an adult and lower amounts for children (see Concerns and Cautions). In short, there is a risk/benefit trade-off when taking high-dose vitamin C.
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