Table Salt Has a Margin of Safety of 1/5

Multiple Choice

Table salt has a margin of safety of 1/5.What does that mean? 

A)  Food additives may use 1/5 of the RDA of dietary sodium. 
B)  One in five people who consume the additive likely will experience health problems. 
C)  People should strive to consume only 1/5 of the UL for table salt each day. 
D)  Five times the amount normally used as a food additive would cause harmful effects. 
E)  One in five forms of table salt have been found to cause health problems.