Possible risk factors for non Hodgkin lymphoma

Some studies have reported that exposure to chemicals used in agriculture can increase the risk of NHL. The chemicals include those used to kill weeds (herbicides) and insects (insecticides or pesticides). Perhaps because of this, we know from research that farmers have an increased risk of NHL. An overview of published studies in 2007 showed an increased risk of NHL in people exposed to pesticides through their work.

Some studies have looked at the use of herbicides, insecticides and pesticides in the home. One recent study showed no increased risk with weedkiller. Others found a significant increase in risk of NHL with household use of pesticides, or in children whose mothers were exposed to pesticides during pregnancy. But this increase in risk is not certain because the studies relied on people remembering which chemicals they'd used and when. We'll need more research before we can be sure if there is, or isn't, a link.

Some studies have linked exposure to solvents to an increased risk of NHL. But, others have not. An overview of the evidence about benzene (a solvent known to cause leukaemia) showed that it can also increase the risk of NHL.

Occupational exposure to radiation has also been shown to increase the risk of NHL.

There is no definite evidence of a link between the use of any type of hair dye and non Hodgkin lymphoma. Some studies have shown an increased risk of NHL in women who use hair dye but other studies have not shown an increased risk. One study even showed a reduced risk. There may be a small link between hair dye use and some types of lymphoma but if there is any increase in risk, it must be extremely small. Research in China and the USA is looking at whether women with certain types of gene changes may be more at risk of developing lymphoma if they use hair dyes.

There is detailed information about hair dye and cancer risk in the questions and answer section.

Scientists have suggested there is a link between a virus called simian virus 40 (SV40) and getting cancer, including NHL. The SV40 virus was found to be in some vaccines in a few parts of the world many years ago. These vaccines are no longer used. The risk has been suggested because the SV40 virus has been found in some NHL cells. But a large study did not find any increased risk of NHL. A recent review of the evidence found no association between SV40 and the risk of any cancer.

One study has linked amfetamines or speed (used to be called amphetamine), LSD or acid (lysergic acid diethylamide) and especially cocaine use to an increased risk of NHL in men. Another study linked amfetamine use to NHL risk, but didn't look at men and women separately. The studies suggest that the longer you use these drugs, the greater the risk. But again, these are only 2 studies and we need more research before we can be certain this is true.

A few research studies have looked at nitrate levels in drinking water. Nitrates may get into drinking water from nitrogen fertilisers used by farmers. So most of these research studies have looked at rural communities.

Nitrates are investigated because we know that they can change into other chemicals inside the body. These are called nitrites. Nitrites can change into N-nitroso compounds, which are known to be cancer causing (carcinogens). The studies looking into NHL risk and nitrates in drinking water are mixed. Some say there may be a risk, while others suggest there isn't.

Some studies show that sunlight may lower NHL risk, but others say the opposite, and at least one shows no effect. Sunlight helps our bodies to make vitamin D, so if sunlight can protect against NHL it may be because people who've been in the sun have higher vitamin D levels in their blood. Another study showed that people with the highest vitamin D levels in their diet had a lower risk of NHL.

Some studies have shown an increased risk of NHL in smokers, but others have found no link.

Two studies have shown that chewing tobacco can increase the risk of NHL, particularly follicular NHL.

Some studies have shown that people who are obese have a slightly higher risk of developing NHL, particularly diffuse large B cell lymphoma, but more research is needed to confirm this.

There is some evidence that people with type 2 diabetes may have an increased risk of NHL. However, more studies are needed to be sure.

One large study showed that people who'd taken more antibiotics during adult life had an increased risk of NHL. But we don't know if this was to do with the antibiotics, or with the illnesses they were treating. Another study showed that people who took statins had a lower risk of NHL. Statins are the drugs to stop blood clots that doctors sometimes give to lower the risk (or after effects) of heart attacks or strokes.

A large analysis of 9 studies suggests that alcohol can lower the risk of NHL. But the picture isn't completely clear. One study showed a lowering of risk in men, but not in women. Another showed a lower risk with wine drinking but not with other types of alcohol. One study found an increased risk in people who drank and also had a family history of cancer. So we will need more research before we know exactly what the relationship is between NHL risk and alcohol.

Some studies suggest that factors that affect a woman’s hormone levels may affect NHL risk. Two studies showed that women who had a higher number of pregnancies had a reduced risk of NHL but another study did not show a link. A reduced risk of NHL has also been shown in two studies for women who are taking, or have taken, oral contraceptives. A recent study showed a reduction in risk of NHL for women who had taken hormone replacement therapy for five years or longer. However, some earlier studies did not show an effect of HRT use on NHL risk, while one study even showed an increase in risk. Overall, findings of studies into hormonal factors and NHL risk are still unclear and we cannot be sure about the effect on risk, if any.