for the prevention of vulvar and vaginal precancerous lesions
as well as for the prevention of HPV-associated anal cancer.
Future studies will determine whether the vaccines also reduce
the risk for head and neck cancers caused by HPV. Early
signs are promising, as a recent study found that vaccination
dramatically reduced oral infection with HPV ( 34).
Even though two highly effective vaccines are available,
the CDC estimates that in 2012 only 33 percent of girls in
the United States aged 13 to 17 years had received the
recommended three doses of HPV vaccine ( 35) (see sidebar
on HPV Vaccine Usage, p. 23). Moreover, coverage has been
reported to be significantly lower among the uninsured and in
several states in which cervical cancer rates are highest and
recent Pap testing prevalence is the lowest ( 33). However,
recent data indicate that despite the low vaccine uptake, there
has been a dramatic reduction in cervical infection with HPV
among girls aged 14 to 19 years since the introduction of
the vaccines ( 36). Thus, research has provided the tools for
dramatic reductions in the burden of HPV-related cancers,
but their use must be fully implemented if they are to have
Energy Balance: Weighing in on Cancer
“Energy balance” refers to the difference between the number
of calories consumed and the number burned. Tipping of this
balance so that a person accumulates excess energy reserves
plays a crucial role in promoting the diseases responsible for
the majority of deaths in the United States: heart disease and
While calories are consumed only through eating and drinking,
they are burned in many ways. Simply existing, breathing,
digesting food, and pumping blood around the body use some
calories. Added to these expenditures are the calories burned
through a person’s daily routine; the more physical activity in a
routine, the more calories are burned.
Although this may seem straightforward, research has shown
that energy balance is, in fact, a complex dynamic (see Figure
12). It is not only influenced by calorie consumption and
There is accumulating scientific evidence that qualitative and
quantitative sleep disturbances increase a person’s risk for
developing cancer. Moreover, it appears that sleep disturbances
increase cancer risk directly and indirectly through their link to
obesity and type 2 diabetes.
Reports that shift workers have a higher incidence of breast,
colorectal, prostate, and endometrial cancers support the
link between sleep disturbances and cancer ( 38-41). Further
evidence to support this link comes from two studies that
indicate that short sleep duration and frequent insomnia increase
postmenopausal women’s risks for colorectal and thyroid
cancers, respectively ( 42, 43).
In addition, recent studies indicate that sleep apnea, which is a
well-established risk factor for cardiovascular mortality, is also
linked with increased cancer mortality ( 44).
Research indicates that there are multiple ways in which sleep
disturbances may influence the development of cancer. One
indirect way is that sleep disturbances increase a person’s
chances of being obese and having type 2 diabetes ( 45, 46), both
of which increase cancer risk. More directly, sleep disturbances
may increase cancer risk as a result of the disruptions to an
individual’s circadian rhythm ( 47); decreases in melatonin
levels ( 48); and disturbances in DNA repair processes ( 49, 50).
Research into the role of circadian rhythms and disease is an
active area of current investigation.
A recent study showed that close to a third of full-time workers in
the United States get six or fewer hours of sleep each night ( 45).
Sleep disturbances are, therefore, likely to become a significant
contributor to cancer incidence. Clearly, more work is needed
to completely understand the causes and develop potential
interventions for this underappreciated cancer risk factor.
Moreover, it is becoming increasingly clear that cancer incidence
and outcomes are profoundly affected by excess energy reserve
accumulation. Importantly, many of the factors that lead to
this accumulation and the consequences of this accumulation
— including obesity, diabetes, metabolic syndrome, and
inflammation — can be corrected by changing personal
behaviors ( 51). Thus, restoring energy balance has the potential
to reduce an individual’s risk of developing cancer and improve
outcomes for individuals already diagnosed with the disease.
It seems likely, however, that a multipronged approach
will be required to disrupt the link between excess energy
reserve accumulation and cancer because behavior change
is challenging for many individuals, for many reasons. As we
discuss below, a promising area of research in this context seeks
to understand how factors affecting energy balance influence
cancer development and outcome ( 51, 52).