Vitamin D levels are linked to mood. The higher your vitamin D, the more likely you are to report higher happiness levels. Equally, you are more likely to report feeling unhappy if your vitamin D is lower. This is demonstrated by the graph below which compares our users who've tested their vitamin D. Those who have good vitamin D levels reported that they were happier (67%) than those who were deficient (42%).
If you're looking for more ways to increase your happiness besides vitamin D, take a look at our 7 ways to feel happier.