Coca-Cola (KO 0.07%) is an incredible business success story and an iconic American brand. The company often serves as a case study on how to build a nearly unassailable competitive position through effective advertising and a relentlessly expanding global distribution system. Yet every investment carries risk, even shares of the mighty Coca-Cola. In that regard, here are three reasons the beverage giant's stock could fall in the year ahead.

The war on sugar
Consumer preferences are shifting, and soda sales are bearing the brunt of that change. Increasingly health-conscious Americans are steadily reducing their consumption of high-sugar drinks, which has led to a decade-long decline in soda sales in the U.S.

Coca-Cola transparently discloses this threat in the risk factors section of its most recent annual report:

There is growing concern among consumers, public health professionals and government agencies about the health problems associated with obesity. In addition, some researchers, health advocates and dietary guidelines are suggesting that consumption of sugar-sweetened beverages, including those sweetened with HFCS or other nutritive sweeteners, is a primary cause of increased obesity rates and are encouraging consumers to reduce or eliminate consumption of such products.

However, here's an example of how some government health agencies have gone about "encouraging" consumers to reduce their soda intake:

Image source: NYC.GOV

Not exactly subtle.

These campaigns have no doubt negatively influenced consumers' perception of sugary drinks. And -- along with the growing public concerns regarding the dangers of obesity -- they are likely continue to adversely impact soda sales in the years ahead.

Slowing growth in emerging markets
So far, these trends have not spread to developing economies -- at least not to the point where they've led to an overall decline in soda sales volumes. Yet unfavorable economic and political conditions in several important international markets are beginning to take a toll.

Coca-Cola earns nearly 60% of its revenues outside the U.S. In addition, much of its volume growth is coming from emerging markets in Asia and Latin America. That makes slowing economic growth in large developing nations such as China and Brazil particularly worrisome.

Furthermore, Coca-Cola is affected to some degree by the events in nearly every major international market. From financial uncertainty in the Eurozone to trade sanctions against countries in the Middle East and Russia, basically anything that serves to undermine consumer confidence and reduce consumers' purchasing power anywhere could lessen demand for Coke's products. 

Foreign currency headwinds
A strengthening U.S. dollar could further lower the value of Coca-Cola's international sales. In 2014, Coca-Cola earned more than $26 billion in revenue from operations outside the United States, and made sales in 70 different foreign currencies. Because the company reports its results in U.S. dollars, it must translate those international financial figures into dollars at exchange rates in effect during each reporting period. If these foreign currencies weaken on an overall basis relative to the U.S. dollar, it negatively impacts Coca-Cola's financial results.

That's exactly what's happened in recent quarters. In the third quarter, fluctuations in foreign currency exchange rates resulted in a 12% hit to operating income and earnings per share. And management expects foreign exchange issues related to the muscular dollar to lower full-year revenue and operating income by 7% and 11%, respectively. 

All told, these negative foreign exchange effects -- combined with changing consumer preferences and slowing international growth -- are likely to weigh on Coca-Cola's share price in the coming year.