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Food, Health, and Eco-news
Sun and Seafood May Curb Lymph Cancers

Vitamin D and omega-3s linked to reduced rates of Non-Hodgkin's lymphomas

by Craig Weatherby

Cancers of the lymphatic systemcalled lymphomasdon't get as much attention as other malignancies, but they kill substantial numbers of Americans.

Unfortunately, rates of the most common kindscalled "non-Hodgkin's lymphomas" or NHLare rising rapidly, for unknown reasons.

Now it's looking like vitamin D and omega-3sboth of which are found most abundantly in fishmay help prevent these cancers.

Sunlight could be our bodies' chief source of vitamin D, but every study shows that Americans don't get nearly enough sun exposure to generate the amounts needed for optimal bone health and cancer prevention.

What is a lymphoma?

The lymphatic system includes the lymph nodeslocated alongside large blood vessels in the neck, underarms, groin, abdomen, and pelvisand other organs that generate immune-system cells, blood platelets, and red blood cells (i.e., the spleen, thymus gland, bone marrow, adenoids, and tonsils).

There are two types of lymphomas: Hodgkin's Disease (HD), which accounts for only one percent of all cancers, and non-Hodgkin's lymphoma (NHL), which constitutes about four percent of all cancers in the US.

Key Points

  • The results of two recent epidemiological studies indicate that dietary and sunlight-generated vitamin D protects against non-Hodgkin's lymphoma (NHL): America's fifth most common cancer.
  • Swedish epidemiological studies link diets high in omega-3s, fiber, fruits, and veggies to reduced risk of NHL.

While the incidence of HD had fallen over the past 20 years, the rate of NHL has risen by more than 70 percent during the same period and is now the fifth most common kind of cancer.

According to the American Cancer Society, some 63,000 new cases of NHL will occur in this country in 2007, and about one in three will die of the disease.

Non-Hodgkin's lymphoma is more common in men, white people, and adults between the ages of 40 and 70, although some types of are among the most common childhood cancers. An American's risk of getting NHL during his or her lifetime is about one in 50.

Aussie and American studies find omega-3s and vitamin D protective

The results of prior research suggest that sun-generated vitamin D offers protection against cancers of the colon, breast, ovaries, and prostate.

And other studies have found that higher levels of vitamin D in the blood and diet are associated strongly with reduced risks of colorectal cancer, and may also reduce the risk of prostate cancer (Kricker A, Armstrong B 2006).

But until recently, it had been widely hypothesized that greater exposure to ultraviolet sunrays would increase the risk of non-Hodgkin's lymphoma (NHL).

However, the results of two epidemiological studiesone from Australia and another from the UScontradict this idea.

Aussies find sun protective

Just over two years ago, researchers at Australia's University of Sydney reported that exposure to sunlight seemed to reduce the incidence of NHL (Hughes AM et al 2004).

The University of Sydney team enrolled 704 adult patients aged 20-74 and 694 healthy controls matched to the cancer patients by age, sex and region. Using questionnaires and telephone interviews the authors calculated the number of hours participants had spent outdoors at 10, 20, 30, 40, 50 and 60 years of age, during working, "non-working" (e.g., outside work and weekend hours), and vacation hours.

Causes and symptoms

The cause of NHL is usually unknown, but people with weakened immune systems appear more vulnerable.

There are about 30 different types of non-Hodgkin's lymphoma, and high-risk groups include those who have received an organ transplant or who have a weakened immune system.

NHL can produce a variety of symptoms, depending on which area of the body is affected:

  • Swollen lymph nodes
  • Fever or copious sweating with night sweats
  • Unexplained weight loss
  • Severe itchiness
  • Coughing or shortness of breath.
  • Stomach pain or swelling
  • Loss of appetite, constipation, nausea, and vomiting.
  • Headache, concentration problems, personality changes, or seizures.

See a doctor if you experience any of these for more than a few days, or with no other explanation such as an infection.

NHL is increasingly treatable by conventional therapies (radiation, chemotherapy, biotherapy, bone marrow transplant). But it makes sense to avoid NHL if possible, and it's looking like diet can help deter the disease.

The results showed that the risk of non-Hodgkin's lymphoma fell as lifetime sun exposure rose. Relative to the lowest quarter of total sun exposure, the people in the highest quarter had a 35 percent lower risk of NHL.

And in some cases, the risk reduction was even higher. Those who reported the most sun exposure on non-working days had a 63 percent lower risk of NHL, while those with the most sun exposure on vacations had 40 percent less change of developing NHL.

All of the sun-related risk reductions were strongest in women and among the participants who reported the greatest sun exposure during their childhood years.

As the Aussies said, “Our results provide strong statistical evidence for an inverse association between sun exposure and NHL” (Hughes AM et al 2004).

While this does not prove that increased vitamin D production in the body is responsible for the sun-related risk reduction, there is no other known factor that would explain the result.

US National Cancer Institute study supports Aussie findings

Last year, researchers from the Division of Cancer Epidemiology and Genetics of the National Cancer Institute published positive findings along the same lines as the Australian investigation's results (Hartge P et al 2006).

They recruited 551 NHL patients and 462 healthy controls, and estimated the risk of NHL relative to UV sunray exposure using four measures:

  • Eye color, which is a marker of susceptibility to UV radiation: that is, the lighter the eyes the lighter the skin, and the more UV rays penetrate it, resulting in higher vitamin D production per hour of sun exposure.
  • Number of hours spent in the mid-day summer sun.
  • Use of sunlamps or tanning booths.
  • Relative ambient UV, based on latitude and climate.

In every case, the risk of NHL went down as sun exposure and UV penetration of the skinhence, vitamin D productionwent up.

The NCI team came to the obvious conclusion: “These data suggest a slight protective effect of sunlight against NHL, and they agree with geographic patterns of NHL incidence observed in the US” (Hartge P et al 2006).

By “…geographic patterns of NHL incidence observed in the US…” they meant that the incidence of NHL is higher in northern, dimmer regions, compared with southern states.

Swedes find omega-3s, fiber, fruits, and veggies protective

We've reported the results of a number of studies conducted by researchers at Stockholm's renowned Karolinska Institute, site of many large cancer studies designed to detect dietary and environmental risk or protection factors.

Last year, they published the results of two highly similar studies, each of which involved about 590 NHL patients and 460 healthy who completed diet questionnaires (Chang ET, Balter KM et al 2006; Chang ET, Smedby KE et al 2006).

In general, the Swedish investigators found no links between dietary intake of various macronutrients (proteins, fats, and carbohydrates) and micronutrients (vitamins and minerals) and the risk of non-Hodgkin's lymphoma (NHL).

The clear winners were omega-3s, fiber, fruits and vegetables, while high consumption of dairy products and fried red meat were associated with increased risk of NHL.

Given the lack of association between diary-heavy diets and cancers, it seems premature to be concerned about the link seen in the Swedish study, as diary intake may be a marker for other dietary trends.

Their analysis produced these positive results with regard to four food factors:

  • Omega-3s: People in the highest quarter of omega-3 intake had a 40 percent lower risk of NHL, compared with people in the lowest intake category.
  • Fiber: People in the highest quarter of fiber intake had 40 percent lower risk of NHL, compared with people in the lowest intake category.
  • Beta-carotene and vitamin E (alpha-tocopherol): Higher consumption was associated with lower risk of NHL.

These results lend support to the anti-cancer value of diets rich in fish, fiber, vegetables, and fruits, and the dangers of diets high in fried foods and red meats.


  • American Cancer Society. Overview: Lymphoma, Non-Hodgkin's type. Accessed online January 26, 2007 at
  • Hughes AM, Armstrong BK, Vajdic CM, Turner J, Grulich AE, Fritschi L, Milliken S, Kaldor J, Benke G, Kricker A. Sun exposure may protect against non-Hodgkin lymphoma: a case-control study. Int J Cancer. 2004 Dec 10;112(5):865-71.
  • Kricker A, Armstrong B. Does sunlight have a beneficial influence on certain cancers? Prog Biophys Mol Biol. 2006 Sep;92(1):132-9. Epub 2006 Feb 28. Review.
  • Hartge P, Lim U, Freedman DM, Colt JS, Cerhan JR, Cozen W, Severson RK, Davis S. Ultraviolet radiation, dietary vitamin D, and risk of non-Hodgkin lymphoma (United States). Cancer Causes Control. 2006 Oct;17(8):1045-52.
  • Chang ET, Balter KM, Torrang A, Smedby KE, Melbye M, Sundstrom C, Glimelius B, Adami HO. Nutrient intake and risk of non-Hodgkin's lymphoma. Am J Epidemiol. 2006 Dec 15;164(12):1222-32. Epub 2006 Sep 27.
  • Chang ET, Balter KM, Torrang A, Smedby KE, Melbye M, Sundstrom C, Glimelius B, Adami HO. Nutrient intake and risk of non-Hodgkin's lymphoma. Am J Epidemiol. 2006 Dec 15;164(12):1222-32. Epub 2006 Sep 27.