Boston , MA —Winter may be a wonderland, but it's also the deadliest time of year for those in the north. Heart attacks and other serious cardiac problems are more common in winter. There's flu to contend with, too. Researchers tend to blame cold weather and poor housing for such seasonal ills, but the January issue of the Harvard Health Letter reports that long nights and vitamin shortfalls may be factors, too.

The eight common winter woes discussed in the January issue include:

Heart problems. In some years and in some countries, deaths and hospitalizations for heart disease and stroke increase more than 50% in winter. Why? Most people blame cold weather, but according to the Harvard Health Letter , there may be other reasons, too, including short days and long nights that throw heart-related hormones out of whack.

Flu. Flu experts think there may be something about winter—besides the fact that we're inside more and thus more likely to share germs—that spurs the flu virus to replicate after lying dormant during the off-season.

Seasonal affective disorder. There may be a cultural component to the clinical depression that afflicts some people in winter. The Harvard Health Letter reports that SAD is relatively uncommon in Iceland and northern Russia , which certainly have plenty of long winter nights.

Hypothermia. Older people are especially susceptible to hypothermia because their bodies don't adjust as well to cold weather. Cases may occur even in relatively mild weather. Wet clothing is a common cause because it wicks away body heat. Alcohol is frequently involved, too. Besides impairing judgment, alcohol opens up (dilates) blood vessels beneath the skin, which creates a misleading sensation of warmth even as body heat escapes.

Carbon monoxide poisoning. About 500 Americans die from accidental carbon monoxide poisoning each year. Many more may feel sick during the winter because of low-level exposure. Poorly maintained furnaces are one cause.

The article also covers frostbite, lack of vitamin D, and problems related to snow shoveling, as well as ways to prevent or treat these winter woes.