Is 100 mcg Too Much for Your Supplement Needs?
                                
                                
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                                    4 min read                                
                            
                                According to the National Institutes of Health (NIH), 100 mcg (4,000 IU) is the safe daily upper limit for vitamin D in adults. Whether 100 mcg is too much depends entirely on the specific substance, as this dose can be harmless for some supplements while dangerously high for others.