Vitamin D Supplementation for Cell Health Found Not to Cause Toxicity (at 40,000 IU Per Day)

By Greg Arnold, DC, CSCS, March 18, 2011, abstracted from “Vitamin D Supplement Doses and Serum 25-Hydroxyvitamin D in the Range Associated with Cancer Prevention” in Anticancer Research

According to the National Cancer Institute, the incidence of cancer in Americans rose from 400 per 100,000 in 1975 to a high of 510 per 100,000 in 1992 and was 461 per 100,000 in 2007 (1). Fortunately, mortality rates from cancer have shown a steady decline over this time period from 51% mortality (201.2 per 100,000) in 1975 to 42% (214 per 100,000) in 1992 and 39% (178 per 100,000) in 2007 (2). Cancer is estimated to cost our healthcare system $228 billion per year (3).

In regards to nutrition and cancer, vitamin D has gained increased recognition as a possible prevention option (4, 5). Now a new study (5) has found that vitamin D supplementation to get vitamin D blood levels into the recommended ranges regarding cancer prevention does not cause toxicity.

The researchers stated optimal vitamin D blood levels to be 40-60 nanograms/milliliter while levels thought to “reduced cancer risk” to be 60-80 ng/mL (5). In the current study, 3,667 subjects (1436 men, 2231 women) between the ages of 38 and 64 provided monthly data on diet and vitamin D intake for 5 years, with researchers measuring intake from both food and supplements. Blood samples were also obtained to measure vitamin D status and to see if any toxicity was observed with the intakes of the patients.

The researchers found:
- 63% were taking up to 500 IU per day and 47% up to 2,000 IU per day.
- Only 1.8% (60 subjects) of the patients reported taking vitamin D intakes between 10,000 and 40,000 IU per day, none of which resulted in any toxic side effects.

It’s important to note the researchers found no toxicity in the 60 patients supplementing over 10,000 IU per day as none reached toxic vitamin D blood levels (200 ng/mL). And while they stated 25% of the patients to not take any vitamin D supplements, they did not state the blood levels of these patients to see if any benefit for vitamin blood levels existed with supplementation.

A point of question, however, comes in their vitamin D recommendations. Although they state “intake of vitamin D in the range from 1,100 to 4,000 IU per day and [vitamin D blood level] from 60-80 ng/ml is needed to reduce cancer risk”, they only make recommendations on achieving a 40 ng/mL blood level (9,600 IU/day), with no intake recommendations to achieve at least 60 ng/mL.

Important information was provided on how vitamin D supplementation affects blood levels. If a patient has a vitamin D blood level of 10 ng/ml then every 1,000 IU per day intake will increase blood levels by 11 ng/ml. However, if the patient has vitamin D levels of 30 ng/ml, then that same 1,000 IU per day will increase it by 8 ng/ml, and only 5 ng/mL if blood levels start at 50 ng/ml.

They went on to conclude that “Universal intake of up to 40,000 IU vitamin D per day is unlikely to result in vitamin D toxicity.”

Greg Arnold is a Chiropractic Physician practicing in Danville, CA. You can contact Dr. Arnold directly by emailing him at or visiting his web site at

1. SEER Cancer Statistics 1975-2007, Table 2.5 - 
2. Age-Adjusted U.S. Mortality Rates By Cancer Site All Ages, All Races, Both Sexes 1975-2007”, FastStats - 
3. “The Economic Impact of Cancer” -
4. Garland CF. Vitamin D for cancer prevention: global perspective. Ann Epidemiol 19: 468-483, 2009. 
5. Garland CF. Vitamin D and prevention of breast cancer: Pooled analysis. J Steroid Biochem Molec Biol 103: 708-711, 2007
6. Garland CF. Vitamin D Supplement Doses and Serum 25-Hydroxyvitamin D in the Range Associated with Cancer Prevention. Anticancer Research 2011; 31(2): 607-611