MADRID (Reuters) - Spanish retailer DIA said on Tuesday its net loss narrowed to 143 million euros ($154.48 million) in the first quarter, from a loss of 151 million a year earlier, helped by lower costs. Core profit jumped to 61 million euros, from 17 million euros, as restructuring costs plunged 92%. Net sales fell 2.1% to 1.70 billion euros, confirming the figure stated by the low-cost supermarket chain retailer in April, as the number of open stores declined and it suffered some negative..