A sweeping new review of scientific studies suggests a strong connection between vitamin D and reduced risk of colorectal cancer, with some findings indicating up to a 58% lower risk among those with the highest vitamin D intake. This revelation, published in April 2025 in the journal Nutrients, could have far-reaching implications for cancer prevention strategies in Thailand and across the globe, offering a natural, affordable, and accessible way to combat one of the world’s most common and deadly cancers (EatingWell).
Colorectal cancer, which includes cancers of the colon and rectum, remains a significant global health issue. It is the second most common cancer among men and the third among women worldwide. In Thailand, colorectal cancer rates have been steadily climbing; it is now among the top five most prevalent cancers in the country. Given that the average Thai diet is shifting towards Western-style patterns, with increased processed foods and reduced fiber intake, urgent attention to prevention is crucial (MDPI).
The recent Nutrients review is particularly compelling because it examined 50 high-quality studies related to vitamin D intake and colorectal cancer risk. Among the highlighted research, the influential Nurses’ Health Study in the United States found that women with the highest vitamin D intake had a 58% reduced risk of developing colorectal cancer compared to those with the lowest intake. Other major studies, such as the Iowa Women’s Health Study and the Spanish PREDIMED study, also found about a 50% reduction in risk among participants with high intake of both vitamin D and calcium. These results held true for vitamin D obtained both from food and from supplements. Notably, a Canadian study involving over 1,400 participants demonstrated that vitamin D supplementation reduced the probability of developing colon polyps—common precursors to cancer—by 33%, and cut the risk of risky polyps by 43%.
How does vitamin D exert its protective effects? According to researchers, vitamin D helps regulate immune function, reduce inflammation, support healthy communication between cells, and promote the natural death of abnormal cells—key mechanisms in halting cancer before it takes hold. It may also reduce tumor growth and limit the formation of blood vessels that feed tumors, a process known as angiogenesis (EatingWell).
Despite some conflicting results in the broader scientific literature—especially around the precise dosage and most effective delivery method (diet versus supplements)—the overall trend points to a robust protective benefit. Notably, a recent nested case-control study from Norway found that low vitamin D levels correlated with a significantly increased risk of proximal colon cancer, particularly when blood levels fell below 50 nmol/L, underscoring the importance of adequate vitamin D especially in women (PubMed NOWAC study). Furthermore, a five-year retrospective cohort study from the University of California reported that patients with higher serum vitamin D after a colon cancer diagnosis had significantly lower mortality rates, with each incremental rise in vitamin D tied to improved survival (PubMed study).
“Vitamin D appears to play a crucial dual role—both in preventing colorectal cancer and in supporting better outcomes for patients already diagnosed,” explains Dr. Siriwan Somjinda, a nutritionist at Siriraj Hospital, who was not involved in the review but regularly advises on cancer-related nutrition. “In a country like Thailand, where sunlight is abundant but vitamin D deficiency remains surprisingly common, especially among office workers and the elderly, these findings are a wake-up call.”
Indeed, vitamin D is widely known as the “sunshine vitamin” because our skin forms it in response to sunlight exposure. Yet, urban Thais often spend much of their days indoors, and concerns about skin cancer and beauty trends emphasizing fair skin lead some to avoid the sun altogether. Pollution, aging, obesity, darker skin pigmentation, and use of sunscreen also reduce the body’s ability to generate vitamin D, creating pockets of deficiency even in tropical countries like Thailand (Times of India).
Adding to the issue, Thai cuisine, while packed with vegetables, traditionally doesn’t feature many foods naturally high in vitamin D. The richest sources are fatty fish such as salmon, mackerel, and sardines, as well as egg yolks and some types of mushrooms, like the popular Japanese shiitake. Fortified foods, such as some brands of milk and yogurt, can also provide a boost. However, the Thai population generally consumes limited amounts of these items compared to Western diets.
For those concerned about vitamin D deficiency, a blood test measuring 25-hydroxyvitamin D is the gold standard. The new research suggests aiming for sufficiency—usually above 50 nmol/L, though international guidelines may vary. If levels are low, health experts recommend safe sun exposure and possibly turning to diet and supplements, but warn against excessive intake, which can harm health.
The Thai Ministry of Public Health has already recognized the importance of vitamin D, especially in connection with bone health in the elderly. However, the cancer-prevention benefits highlighted by this new research could encourage a fresh round of public health campaigns—similar to successful campaigns against iodine deficiency or salt overuse in the past. Dr. Weerapong Pongsuwan, Deputy Director of the National Cancer Institute of Thailand, notes: “Encouraging Thais to check their vitamin D status—especially those at higher risk, such as the elderly, people with obesity, or those with a family history of colorectal cancer—could be a cheap yet effective way to save lives. We recommend a diet high in fish, eggs, and fortified dairy, alongside regular, careful sun exposure.”
Globally, vitamin D deficiency is estimated to affect 30-50% of people, with even higher rates in certain communities. Known risk factors for colorectal cancer overlap significantly with vitamin D deficiency—older age, diabetes, a sedentary lifestyle, poor gut health, high processed food intake, and lower education or income. This is particularly relevant in Thailand’s rapidly aging and increasingly urban population.
Cultural attitudes may need to shift, too. Traditional Thai wisdom about getting up early for sunlight has new scientific backing in the fight against cancer. Incorporating “เดินรับแดดเช้า” (dernn rap daet chao—taking a morning walk in the sun) can be a helpful, localized strategy.
As for future research, scientists call for large-scale randomized trials tailored to Asian populations, including Thais, to determine the optimal vitamin D intake and distribution for the region. Questions remain around the preferable sources (food, supplements, or sunlight), possible risks of over-supplementation, and the interaction between vitamin D and other dietary or genetic factors unique to Southeast Asia. Meanwhile, guidelines may soon evolve to explicitly include cancer prevention when recommending vitamin D levels—a policy change that could have echoes throughout hospitals and clinics, from Bangkok to Buriram.
For Thai readers, the actionable advice is clear: don’t overlook vitamin D. Get your blood levels checked, especially if you are over 50, have risk factors for cancer, or spend most of your day inside. Embrace a diet richer in fish, eggs, and fortified foods, and—where it’s safe—sen yang daet (soak up the sun). School cafeterias and workplace canteens could support this by expanding menu options that include vitamin D–rich ingredients. For policy makers, investing in national screening programs and fortifying basic foods could be a powerful next step in the fight against cancer.
The bottom line is that, in the words of one expert cited in the review, “Vitamin D is one of the cheapest, safest, and most accessible interventions we have.” As further research unfolds, the hope is that more Thais will harness the sunshine vitamin to guard their health, not only for stronger bones but for a cancer-free future.
Sources:
- EatingWell summary and full article
- MDPI review: Vitamin D and Colorectal Cancer Prevention
- Yahoo News on Vitamin D and Cancer Risk
- Times of India on Vitamin D Deficiency
- Recent academic studies on vitamin D and colorectal cancer from PubMed