By: Rachel Namery, MS Nutrition Science
What is Vitamin D and What Does it Do?
Vitamin D is a fat-soluble vitamin found in small amounts of some foods, added to some food, and available as a dietary supplement. It also produced by the body when UV rays from sunlight hit the skin and trigger vitamin D synthesis. Vitamin D that is obtained from the sun, food, and supplements is inert in the body and must undergo 2 hydoxylations within the body for activation. The first happens in the liver and converts Vit D into 25-hydroxyvitamin D, also known as calcidiol. Then the second step occurs primarily within the kidneys and forms the biologically active form of 1,25-dihydroxyvitamin D, known as calcitriol.
Vitamin D promotes calcium absorption within the gut and helps to maintain proper levels of serum calcium and phosphate concentrations to help normal mineralization of bone and to prevent hypocalcemic tetany. It is also used for bone growth and bone remodeling by the osteoblasts and osteoclasts. Without the proper levels of vitamin D, the bones can become thin, brittle, or misshapen. Vitamin D sufficiency helps prevent rickets and osteomalacia in children and adults respectively. Together with calcium, vitamin D helps to protect older individuals form osteoporosis.
Vitamin D also has other roles within the body of which include modulation of cell growth, neuromuscular and immune function, and also the reduction of inflammation. Many genes that are responsible for encoding proteins that regulate cell proliferation, differentiation, and apoptosis are also modulated in part by vitamin D. This role of role of vitamin D is primarily what this article focuses on.
Vitamin D as a protective tool against colorectal cancer?
A new meta-analysis of 17 studies found vitamin D levels < 40 ng/ml and increased increased risk for colorectal cancer.
What is Colorectal Cancer?
Colorectal cancers are any cancers that start in the rectum or colon. These cancers usually start as polyps, or growths, on the innermost lining of the rectum or colon. Like many cancers, this type can spread very quickly and grow to all the other layers of the colon and rectum; other times it is indolent. The American Cancer Society predicted that 1 in 21 men and 1 in 23 women in the United States will develop some type of colorectal cancer throughout their lifespan and over 50,000 people die from this cancer every year. This is an alarming number. Once this cancer spreads it needs to be treated aggressively via chemotherapy, radiation or other invasive therapies. Some risk factors for colorectal cancer include, genetic predisposition, lifestyle (diet, smoking, inactivity), type II diabetes, obesity and a history of polyps. Thankfully, there is something you can do to help protect yourself against developing colorectal cancer, even if you are at an increased risk from other factors.
Vitamin D and Colorectal Cancer
Studies show a connection between vitamin D status and colorectal cancer. One meta analysis showed an inverse relationship between vitamin D levels and risk of colorectal cancer. They also found that patients who had colorectal cancer experienced improved survival rates if they had a higher vitamin D status.
A recent article pooled 17 cohort studies and evaluated the research on circulating vitamin D status and risk of colorectal cancer. The 17 cohort studies consisted of 5,706 participants with colorectal cancer case and 7,107 controls who all had varying levels of circulating 25(OH)D. They considered vitamin D deficiency as levels below 12 ng/mL (30 nmol/L), sufficiency as levels between 20-25 ng/mL (50-62.5 nmol/L), and optimal levels ranged between 30-40 ng/mL (75-100 nmol/L).
● Vitamin D levels below 12 ng/mL was associated with a 31% increased colorectal cancer
risk (RR: 1.31; CI: 1.05-1.62).
● Those with vitamin D levels between 30 – 34.9 ng/mL experienced a 19% decreased risk
of developing colorectal cancer (RR: 0.81; CI: 0.67 to 0.99).
● Vitamin D levels between 35-40 ng/mL was associated with a 27% reduced risk of
colorectal cancer (RR: 0.73; CI: 0.59-0.91).
● They also found in women, for each 10 ng/mL (25 nmol/L) increase in circulating vitamin
D, there was a 19% decreased risk of colorectal cancer.
The researchers concluded,
“Optimal 25(OH)D concentrations for colorectal cancer risk reduction, 75-100 nmol/L (30-40 ng/ml), appear higher than current IOM recommendations.”
The findings showed that the inverse relationship of 25(OH)D and risk of colorectal cancer was statistically significant in women (p < 0.001) but not statistically significant in men (p = 0.20). This analysis suggests that colorectal cancer risk decreases as circulating 25(OH)D increases up to 40 ng/mL (100 nmol/L).
Vitamin D Council recommendations
Supplementing with 5,000-10,000 IU vitamin D3 per day may help reduce one’s risk of colorectal cancer. If levels > 40 ng/ml they are possibly more protective, however, like in breast cancer, no studies have addressed it.
McCullough,M et al. Circulating vitamin D and colorectal cancer risk: an international pooling
project of 17 cohorts .Journal national cancer institute, 2018