Shares of nutritional supplement maker Herbalife ( HLF) plummeted Friday after the company lowered its sales and earnings expectations for the first quarter of 2007. The stock sank 19.5% to $31.65 after an announcement of its guidance along with preliminary fourth-quarter results after the close of trading Thursday. Herbalife expects to report sales of between $482.7 million and $484.7 million in the most recent quarter, representing an increase of 18% to 18.5% over the prior year. On the basis of those results, the company anticipates fourth-quarter earnings within its previously guided range of 52 cents to 55 cents a share, excluding charges related to business strategy changes. For all of 2007, the company is reaffirming its previous guidance of $2.40 to $2.47 in earnings per share excluding certain expenses. However, those results would reflect sales growth of between 6% and 10%, combined with improved operating margins and a lower tax rate. The company previously expected a 10% to 15% increase in sales. Looking at current sales trends, the company predicts slower sales growth in Mexico than it previously estimated. Those results should be partially offset by sales growth in the U.S. and several other countries, the company says. Herbalife expects to earn 50 cents to 55 cents a share in the first quarter of 2007, excluding expenses related to its so-called realignment for growth initiative. Analysts surveyed by Thomson First Call were expecting the company to earn 58 cents a share in the quarter.