Women ages 18 to 44 had the highest rate of fatigue – just over 20 percent.

Being tired is linked to something deeper than just overwork or a sign of the times. I'm a registered dietitian and nutritional neuroscientist. My research, along with the work of others in the field, shows that your diet and lifestyle choices may contribute to your struggles.

These two factors are closely interconnected and could be the key to understanding what's holding you back.

In particular, not getting enough of three essential nutrients – vitamin D, vitamin B12 and omega-3 fatty acids – is linked to low energy levels.

Vitamin D

More than 40 percent of adult Americans are deficient in vitamin D. Low levels are linked to fatigue, bone pain, muscle weakness, mood disorders and cognitive decline.

Foods high in vitamin D include fatty fish like salmon, sardines, freshwater rainbow trout, fortified dairy products and egg yolks. Among the sources for vegetarians and vegans are fortified plant-based milks and cereals and some kinds of mushrooms.

The US government's recommended daily amount of vitamin D is 400 international units, or IU, for infants up to 12 months, 600 IU for people ages 1 to 70 and 800 IU for people over 70. Just over 5 ounces (150 grams) of sockeye salmon fillet has about 800 IU of vitamin D. If you are low in a vitamin, your doctor may prescribe you a higher dose than the recommended daily amount to elevate your blood levels to normal.