There will be many potential reasons for post-holiday torpor, most of them fairly obvious -- from saying goodbye to loved ones we won't see for some time, to loosening belts and paying bills. But if after tallying the obvious you still can't fully account for your lassitude, somewhat less obvious explanations deserve consideration as well. Two hormones figure prominently among the relevant suspects.
The first is vitamin D.
In general, a nutrient is something we must ingest and metabolize. We usually burn nutrients, or their breakdown products, as fuel; or use them to build a part of ourselves. By and large, nutrients are either fuel, or construction material.
Hormones are neither. If a nutrient is fuel, a hormone determines how much gets tossed on the fire. If a nutrient is construction material, a hormone may be both builder, and architect. Hormones are regulators of body function. They travel through the blood stream, bind to receptors throughout the body, and exert effects far removed in place, time, and character from their origins.
Which brings us back to vitamin D. We have long been preoccupied with vitamin D as a nutrient because of its prominence in the recent history of public health. In the latter part of the 19th and early 20th centuries, there was a massive shift of the workforce -- including young children -- from farm to factory. Factories in Europe and the U.S. routinely involved work from before dawn to after dusk with an abrupt decline in ambient sun exposure resulting.
At the time, the effects of sunlight on skin were the almost exclusive source of vitamin D, so no sun meant vitamin D deficiency. This manifested as an epidemic of rickets -- a stunting condition of impaired bone growth in children. The epidemic ended when the cause was identified, and dairy products were fortified as they still are with vitamin D. We have focused on vitamin D as a nutrient rather than a hormone, and on its specific effects on bone, ever since.
Only recently has that begun to change, as the scientific literature has filled up with studies suggesting other important effects of vitamin D. That there is controversy in this area is indicated by the recent IOM report on vitamin D intake, which many, myself included, think may have erred to the low side. Be that as it may, there is no doubt that vitamin D affects not just bone, but also the immune system, muscle, the cardiovascular system, and the brain.
Whether or not vitamin D directly affects mood -- from seasonal affective disorder to depression -- is uncertain. Many people are prone to the 'blues' during the short, dark days of winter, and prone to low vitamin D levels at the same time. Vitamin D deficiency may be a cause, or both may simply be effects, in turn, of sunlight deficiency. Whatever its role, vitamin D deficiency is common; some studies suggest that well over a third of the U.S. population is affected at any given time.
As research advances to sort out the details, you might as well hedge a bet in your favor. I recommend a vitamin D level near the middle of the normal reference range for the population. When I check my patients here in CT, I find that quite a few have low levels year round, but particularly in winter. If a supplement is needed to approximate the middle of the bell curve, this is one of the few I routinely do encourage. Your doctor can help determine how much you need to reach, and remain, at the target level.
Thyroid hormone is less directly tied in with the sun, but even more directly connected to mood and energy. Its reputation as a master regulator of body functions is well deserved -- there is little the body does that is not influenced by the thyroid.
Roughly 5 percent of the U.S. population develops overt hypothyroidism, the risk rising as we age, and higher in women than men. But up to four times as many may experience "sub-clinical hypothyroidism." In this condition, thyroid hormone levels are actually normal- but the pituitary gland is working overtime to keep them so. The characteristic lab results for this state are an elevated level of thyroid stimulating hormone (TSH) from the pituitary, and low normal levels of thyroid hormones.
But normal means within the normal range for the population, not necessarily normal for you. While we all tend to fall somewhere in the wide population bell curve, only a narrow range of it really tolls "normal" for any one of us. Somewhere in that curve is the spot our hormones prefer to call home.
Vitamin D, thyroid hormones, and/or TSH, can be technically in the normal range for the population (each laboratory will have its own), but still not quite right for you. If not feeling like you think you should -- if tired, or groggy, or apathetic, or blue -- confer with your doctor to determine if getting these hormones more at home might be all or part of the solution.
Make your hormones feel more at home, and they are apt to return the favor. There's no place quite like it.
Follow David Katz, M.D. on Twitter: www.twitter.com/DrDavidKatz