The new study, published in Cancer Prevention Research, suggests vitamin D could offer a “very strong, very significant protective effect" over endometrial cancer in obese female lab mice - which could translate into a protective effect in humans.
"Vitamin D has been shown to be helpful in a number of cancers, but for endometrial cancer, our study suggests it protects only against cancer that develops due to obesity," said Dr. Leena Hilakivi-Clarke, lead investigator of the research and Professor of Oncology at Georgetown University.
"If these results are confirmed in women, use of vitamin D may be a wonderfully simple way to reduce endometrial cancer risk,” added Hilakivi-Clarke.
Vitamin D and the big C
Endometrial cancer is the fifth most common cancer among women, with over 41,000 new diagnoses in the US during 2006.
Exposure to high estrogen levels is the main risk for endometrial cancer. Another major factor is obesity, which is known to elevate chances of developing the cancer by between three and five fold.
The connection between vitamin D intake and cancer protection dates from the 1940s when Frank Apperly demonstrated a link between latitude and deaths from cancer - suggesting that sunlight gave "a relative cancer immunity". Since then numerous studies have suggested associations between vitamin D and lower risks of many cancers.
The new research investigated the potential for dietary vitamin D3 to inhibit endometrial cancer in mince.
Decreased incidence
The researchers reported that vitamin D3 did not affect endometrial cancer risk, but did inhibit obesity-induced endometrial lesions.
Dietary vitamin D3 decreased the incidence of endometrial pathology in obese mice by 42 percent, and was observed to alter endometrial expression of key enzymes and receptors in the mice – including estrogen receptor-α and progesterone receptor protein levels.
Protective effect?
The researchers warned that the potential protective effect of vitamin D3 against endometrial cancer in humans remains controversial, as the interactions between vitamin D3, obesity, and endometrial cancer have not fully been studied.
"Since over 50 percent of women in the US are overweight or obese ... other means are needed to prevent endometrial cancer in these women ...Vitamin D supplements are likely to be safer than, for example, progesterone," said Dr Hilakivi-Clarke
She added that, as yet, researchers do not know why vitamin D reduces endometrial cancer risk only in obese animals, but noted that data suggests that these mice produce less osteopontin – a cancer aggravator - and more E-cadherin – which stops cancer from metastasizing.
"We really don't know why dietary vitamin D works so well in our obese mice,".
"We are currently investigating the mechanisms, and we are hopeful that we can find an answer," said Hilakivi-Clarke.
"Until further studies are done, I think the best advice for women concerned about their risk is to take vitamin D supplements or spend a few more minutes each week in the sun,” she added.
Source: Cancer Prevention Research
Published online ahead of print, doi: 10.1158/1940-6207.CAPR-10-0088
“Dietary Vitamin D Exposure Prevents Obesity-Induced Increase in Endometrial Cancer in Pten+/− Mice”
Authors: W. Yu, M. Cline, L.G. Maxwell, D. Berrigan, G. Rodriguez, A. Warri, L. Hilakivi-Clarke