Higher risk, yes. But higher death rate? Can you provide evidence? It's actually hard to measure.

Airline pilots and people living at high altitudes do have a slightly higher radiation exposure and thus a slightly higher cancer risk. Two New York Times articles on this are here and here. The most recent, definitive info on low level radiation risks is provided in a series of National Academy of Sciences reports (the latest is here). Our best data on low level radiation exposure risks is from the survivors of Hiroshima and Nagasaki, so more recent reports represent fine-tuning of the risk rate.

To quote from the 1990 article: "among 100,000 crew members who spent 20 years flying 960 hours a year on an east-west domestic route of more than three hours, 59 to 61 ''premature cancer deaths'' would occur. Among 100,000 passengers flying 480 hours a year on the same route, or about 9 hours a week, 29 or 30 additional cases of cancer would occur. The rate of cancer from all causes would be about 22,000 in that group."

Now nobody would argue that additional deaths are something we want! But how would you measure it? Let's imagine doing a study of 10,000 pilots over their lifetime. You'd expect 2200 to die of cancer from non-radiation causes, and the statistical fluctuation on that number is sqrt(2200)=46, meaning that about 2/3 of the time you'd measure between 2200-46 and 2200+46 (this is standard small-N statistics, which is why if you flip a coin 20 times you don't always get exactly 10 heads). The excess cancer deaths due to radiation from flying is 6 per 10,0000. So how do you reliably tell that you have 6 additional deaths? And of course you have to try to adjust for the real and significant health risks: are pilots more or less obese than the average population, and do they smoke cigarettes more or less?

If you increase the study size to 100,000 you have a statistical fluctuation of sqrt(22000)=148, and an additional number of deaths of 60. Again, you can't really tell. Increase the study size to a million and then you can start to tell something, as long as you can properly correct for all other major variations in risk like weight and smoking history.

The point is that the health risk from the small, extra radiation exposure received at altitude is very small, and very small effects are actually quite hard to measure in epidemiological studies.

Plus another point: hearsay anecdote is not solid evidence.