Emerging studies suggest keeping vitamin D levels in a healthy range may reduce colorectal cancer risk. A broad review of more than 50 adult studies, including data summarized in Nutrients, shows that people with vitamin D deficiency have a higher likelihood of developing colorectal cancer than those with sufficient levels. This topic resonates in Thailand where cancer awareness and vitamin D deficiency are receiving growing attention.
Colorectal cancer remains a major health challenge in Thailand, ranking among leading causes of cancer death, especially for men and women over 50. Worldwide, about 1.2 million new cases are diagnosed each year. In Thailand, urbanization, shifts toward processed foods and red meat, and an aging population contribute to rising numbers. Awareness of preventive behaviors and regular screenings varies, particularly outside major cities. At the same time, vitamin D deficiency—often called the sunshine vitamin due to sun-driven production—has become more common, even in sunny Southeast Asia. Urban indoor work, air pollution, skin-protective practices, and diets lacking vitamin D-rich foods contribute to this gap. Global data indicate 30–50 percent of people may not get enough vitamin D, with higher deficiency among women, older adults, and individuals with darker skin.
New research involving tens of thousands of participants indicates vitamin D’s health benefits extend beyond bones. A large review published in 2025 found that higher blood levels of vitamin D—whether from diet, supplements, or sun exposure—were linked with as much as a 58 percent lower risk of colorectal cancer compared with the lowest levels. Long-running studies, including cohorts similar to the Nurses’ Health Study, support this association. Experts attribute part of the effect to vitamin D’s role in reducing inflammation, promoting normal cell differentiation, encouraging cancer cell death, and stabilizing the gut environment. An authority on cancer prevention notes that observational data consistently support vitamin D’s protective role, even as some randomized trials yield mixed results.
How might vitamin D help prevent colorectal cancer? Medical professionals explain that vitamin D modulates immune function and acts on colon tissue through the vitamin D receptor. Activation of this receptor influences gene expression linked to cell growth and death, processes central to cancer suppression. A deficiency may blunt these protections, potentially increasing risk when intestinal inflammation is present.
Despite these encouraging findings, experts do not yet endorse universal vitamin D supplementation as a cancer prevention strategy. While correlations are strong, they do not prove that supplementation alone reduces cancer risk. Lifestyle, genetics, and gut health all influence outcomes. Still, specialists advise regular vitamin D checks for those at risk of deficiency—older adults, people with limited sun exposure, individuals with darker skin, and those with chronic health conditions or digestive disorders. In practical terms, maintaining optimal vitamin D levels and adequate dietary intake is considered important for colorectal cancer prevention and improving prognosis.
Thai society can take practical steps. Sunlight remains the best natural source: a modest amount of direct sun on arms and legs a few times per week, outside peak UV hours, can boost vitamin D production. However, cultural practices that shield skin, urban living, and pollution can limit this benefit. Thai diets often rely on rice, pork, and chicken and may lack natural vitamin D sources such as fatty fish, egg yolks, and fortified dairy. Urban lifestyles and breakfast skipping can further reduce fortified foods. These factors may contribute to higher deficiency than commonly assumed, and supplement use is not yet widespread.
Recommended daily targets vary. The US NIH suggests 600 international units (IU) for adults under 70 and 800 IU for adults 70 and older. Some experts favor 1,000–2,000 IU daily for those at risk, but medical supervision is advised. A simple blood test can determine status before starting supplements. Excessive intake can cause adverse effects, so moderation and supervision remain essential.
Besides sunlight, diet plays a key role. Rich sources include cod liver oil, trout, salmon, sardines, tuna, certain mushrooms, egg yolks, and fortified dairy or cereals. The Mediterranean-style diet—high in fish, healthy fats, fruits, and vegetables—aligns with protections against both vitamin D deficiency and colorectal cancer. Thai dishes such as mackerel-based salads and Southern rice salads can be adapted to boost vitamin D naturally through local fatty fish and fresh produce.
For those already diagnosed with colorectal cancer or in remission, maintaining adequate vitamin D levels may support better outcomes and immune balance. Recent umbrella reviews suggest improved prognosis with sufficient vitamin D, along with better regulation of inflammation during treatment. Canadian research cited in reviews indicates vitamin D supplementation could reduce polyp development by about one-third and high-risk adenoma formation by more than 40 percent, signaling potential early prevention benefits.
However, large-scale randomized controlled trials are still needed to confirm causality across diverse populations, including Thai subgroups with distinct lifestyles. Vitamin D should complement, not replace, a healthy lifestyle and regular screenings, such as stool tests or colonoscopy, especially for those over 50 or with a family history.
Thailand’s public health focus has traditionally emphasized mass screenings, vaccinations, smoking cessation, and infectious disease control. Nutrition has centered on undernutrition, obesity, and diabetes. Addressing silent micronutrient deficiencies and their links to cancer is a newer, evolving area for Thai preventive policy. The Ministry of Public Health could consider pilot programs to raise awareness about vitamin D in urban settings and explore blood-testing accessibility for at-risk groups.
Looking ahead, vitamin D’s role as a modifiable risk factor for serious diseases is likely to grow in Thailand as public concern about non-communicable diseases rises. Colorectal cancer remains a significant national health issue, and even small preventive gains could save many lives over time. Ongoing research in Thai populations will add valuable data to global findings and help tailor local recommendations.
Practical guidance for Thais who want to reduce colorectal cancer risk:
- Check vitamin D status regularly with medical guidance.
- Incorporate vitamin D–rich foods into daily meals—salmon, mackerel, egg yolks, fortified dairy.
- Get safe sun exposure in moderation and be mindful of UV protection.
Vitamin D is a part of a broader health strategy. It is not a substitute for screening, and lifestyle choices—regular exercise, balanced diet, limited alcohol, and avoidance of tobacco—remain essential.
For further context, researchers point to ongoing studies in Nutrients and Prevention, along with EatingWell coverage, to deepen understanding of vitamin D’s role in colorectal cancer. If you have specific health circumstances, discuss a personalized plan with your primary care provider, including whether a vitamin D test and dietary adjustments are right for you.