I found an interesting overview of the health risks of aircraft crew and frequent flying passengers. Here is a link to the article Risk Factors, Health Risks, and Risk Management for Aircraft Personnel and Frequent Flyers

I made up a summery of the contents of this article, which also includes indications for risk management:

The article reviews health risks and risk factors associated with air travel, and discusses risk management strategies. To reduce adverse health risks, risk factors such as radiation, infection, stress, temperature, pressure, and circadian rhythm need to be avoided or reduced to levels that are as low as technologically achievable to protect flight personnel and passengers.Risk factors and health risks

In general, flight-crew personnel and passengers are exposed to a variety of risk factors, including: 

1. Physical stressors: Electromagnetic fields (EMFs), and ionizing radiation of cosmic origin (protons, neutrons, and γ-radiation), which are at appreciably higher levels than at ground level.
2. Chemical stressors: Chemical pollutants and environment agents at altitude, such as ozone, the combustion products of jet fuels (e.g., CO, CO2, polycyclic aromatic hydrocarbons [PAHs], etc.), and the chemicals used to construct the interior of aircraft, are sources of exposure. In a closed aircraft, it is important that a clean supply of air is maintained from the exterior.
3. Biological stressors: Food poisonings might occur due to the consumption of foods contaminated with microorganisms, such as Escherichia coli, vibrios, Salmonella, and Serratia marcescens. Legionella species are also often detected in flight (Ott et al., 2004), and micro-organisms such as those of flu and tuberculosis may be transmitted from infected individuals to healthy people through aircraft air filtering systems.
4. Psychological stressors: Stress is characterized by non specific adverse biological responses to emotional disturbances, tiredness, and the disruption of circadian rhythm before, during, and after flight. Immune functions are altered in stressful situations, and these increase the likelihood of infection.
5. Others: Other risk factors due to the aviation environment include acceleration forces, disorientation due to irregular flight, hypoxia, noise, and changes in pressures and temperatures.

Cosmic radiation
At high altitude, which is the domain of commercial airliners, cosmic-ray exposure rates are hundreds of times greater than at ground level. A crew member who works 1100 block hours (a flight begins when the aircraft leaves the blocks before takeoff and ends when it touches the blocks after landing) per a year would receive an annual radiation dose between 0.3 and 9 mSv. The higher value, 9 mSv (microsievert), is less than the occupational exposure limit of 20 mSv recommended by the International Commission on Radiological Protection. However, for pregnant women, the ICRP recommended that occupational exposure to ionizing radiation should not exceed 2 mSv.

Epidemiological evidence
Epidemiological evidence shows that airline astronauts, pilots, and cabin attendants are at high risk of cancer, cardiovascular diseases, cataract, psychosis, hearing loss, infection, and developmental disorders. 

Many epidemiological studies support the association between flight personnel and cancer risk by demonstrating elevated levels of micronuclei and cytogenetic aberrations, using techniques such as fluorescent in situ hybridization (FISH) (Scheid et al., 1993; Heimers, 2000; Romano et al., 1997; Cavallo et al., 2002). A meta-analysis of all follow-up studies that reported standardized incidence ratio (SIR) for cancer among female flight attendants was performed by applying Bayesian hierarchical models, and showed significant excesses of melanoma and breast cancer (Buja et al., 2006). In male pilots, relative risks (RRs) were also elevated for mortality from melanoma and for the incidence of prostate cancer in another meta-analysis (Ballard et al., 2006).

After a review of 20 relevant epidemiological investigations, Ott and Huber (2006) reported that crew members and frequent flyers may be at higher risk of developing cancers of the skin (e.g., malignant melanoma, basalioma, etc.), prostate cancer, or leukemia. 

Risk management

Strategies for risk management to reduce risk factors and health risks are summarized as follows.

1.     Reduction of cosmic rays:

• To reduce exposure levels to cosmic radiation to as low a level as technologically achievable (ALATA) or as low as reasonably achievable (ALARA), one of the best solutions is to fly less frequently or to take longer intervals between flights, thus increasing recovery times. The second solution is to fly safer routes based on the computational estimation of cosmic radiation levels. In terms of this approach, safer flight routes should be developed.
• To develop radiation resistance aircrafts using high technology. Cosmic radiation could be blocked more effectively if, for example, metallic lead was used in aircraft construction. New radiation-resistant materials should also be developed for this purpose.

2.     Maintenance of good quality air and a clean environment:

• The maintenance of good air quality is important. Smoking is prohibited in cabins by law, and should be monitored closely to ensure that the rules are complied with. Air cleaning systems should be equipped and maintained properly.
• It is necessary to keep optimal oxygen concentrations and comfortable temperatures and pressures in flight.

3.     Avoidance of micro-organism contamination:

• Careful examination of all possible items (e.g., foods, blankets, pillows, water, baggage) is imperative to prevent cabins becoming contaminated with microorganisms.
• Foods need to be boiled or heated before serving, and all cutlery should be sterilized.

4.     First aid and health professionals:

• In cases of emergency, first aids and drugs should be provided.
• Health professionals such as doctors, pharmacists, and nurses could assist if available. Other alternatives include telemedical services from health professionals.
• Cabin attendants in stressful situations should be advised to take antioxidant vitamins. To reduce or to prevent the health risks associated with frequent flyers, supplementation of antigenotoxic agents or antioxidants could be recommended, because these agents are known to block or prevent the formation of chromosomal aberrations and oxidative DNA damage, and immune suppression.

5.     Management of mental or physiological stress:

• Exercise is a good choice for the management of stress. However, moving around in a closed cabin is difficult, but a yoga type of exercise could be easily performed and should be recommended for a short period of time (20-30 min). In particular, stretching and massage could be highly effective at promoting the circulation, and for rejuvenation and muscle relaxation.
• Sound and sufficient sleep is one of the best ways of managing stress. Sometimes, passengers rely on drinking alcohol as a sleeping aid, but this may aggravate a physical or mental condition and deplete vitamins and nutrients in the body. Sleeping pills should be taken under medical advice in limited situations.

6.     Risk communication and perception:

• Crews and passengers should be informed of what the risk factors and the expected health risks of flying are. Airline companies should be aware of the seriousness of this issue, and should invest enough money to reduce or avoid risks associated with flight.
• If crews and frequent flyers are aware of the risk factors and health risks, they may be able to manage them more effectively. Thus, the role of risk communication to different parties (e.g., consumers, companies, government, toxicologists, lawyers, politicians, etc.) involved in this issue is important, and needs to be undertaken on a cooperative basis.

Source: Risk factors, health risks, and risk management for aircraft personnel and frequent flyers.
Journal of toxicology and environmental health. Part B, Critical reviews [1093-7404] Kim yr:2007 vol:10 iss:3 pg:223 -34