What's the difference between Kelp / Seaweed / algae / plankton? Do they all have vitmin D?

'friendof' is a liar. I've been diagnosed by severe vitamin D deficiency and have to take at least 1000U daily(capsules) with calcium. Vitamin D is synthesises with exposure to sunlight and hence most people need supplements at least in winter. Blacker people are also more likely to suffer from deficiency.

It can cause extreme depression and fatigue.

Only very very little of vitamin D is obtained from food.

None of them do. Mushrooms are the only natural plant source. Milk is a great vegetarian source of vitamin D, if you drink it. Soy and rice milks, OJ and cereals are often fortified with it. There are also supplements. Be sure the one you choose is labeled vegetarian if you go that route.

There is a common myth that you get lack of vitamin D without meat or sun. In fact a lot of recent studies have found that it's exaggerated, the Vitamin D lack. Either than that, eat fortified stuff.

I might supply myself my dream apartment with an fantastic view, a new vehicle for my husband, after which i might do anything like world peace. Then i might start giving myself stuff once more :)