No supplements necessary.

Omega-3 DHA supplements have been shown to raise LDL cholesterol levels.

Here’s the conclusion of the study below:

In the absence of convincing evidence for the deleterious effects resulting from the lack of DHA from the diet of vegetarians, it must be concluded that needs for omega-3 fatty acids can be met by dietary ALA.

DHA Status of Vegetarians, Prostaglandins, Leukotrienes, And Essential Fatty Acids, August – September 2009

ALA is alpha-linolenic acid, an omega-3 (n-3) fatty acid found abundantly in plant food. The body uses it as a substrate to make EPA and DHA. Here’s a list I made in a prior post (A Vegan Can Get Enough Omega-3 Without Taking A Supplement) of the total omega-3 content of some common plant-based foods, most of the n-3 is probably in the ALA form. Even very low-fat foods like spinach and cauliflower contain respectable amounts of omega-3.

Walnuts, 7 halves, 1282 mg
Flaxseed, ground, 1 teaspoon, 570 mg
Chia seeds, whole, 1 teaspoon, 350 mg
Kidney Beans, boiled, 252 mg
Frozen spinach, 1/4 cup, 176 mg
Brussels sprouts, 1/2 cup, boiled, 135 mg
Cauliflower, 1/2 cup, boiled, 104 mg
Broccoli frozen, not cooked, 82 mg
Pistachios, raw, 25 nuts, 36 mg
Oatmeal, dry, 1/3 cup, 27 mg
Red sweet pepper, 1/2 cup, 19 mg
Zucchini, 1/2 cup, cooked, 12 mg

Here are a few more bits from that study. On cardiovascular disease:

It has been postulated that an increased intake of DHA may decrease risk of cardiovascular disease, possibly by affecting the susceptibility to cardiac arrhythmia [31]. However, obesity/overweight is less common in vegetarians and vegans than omnivores and blood pressure tends to be lower [32]. Serum total and LDL cholesterol concentrations are also lower among vegetarians and especially vegans [2,8,15] compared with meat eaters, which would retard the development of atherosclerosis. This observation is consistent with the favorable effect of a strict vegetarian diet on atherosclerosis progression [33].

DHA supplements can increase LDL:

It is notable that Geppert et al. [10] reported a 6.9% increase in LDL cholesterol with 0.9g DHA/d in vegetarians. We reported a 7.1% and a 10.4% increase in LDL cholesterol with 0.7 and 1.5g DHA/d in omnivores [35,36], respectively.

On cognition:

Giem et al. [39] were unable to demonstrate any increase in risk of dementia in Seventh Day Adventist vegetarians. Furthermore, we have been unable to find any evidence of cognitive impairment [40] in vegan men — the National Adult Reading Test [41], which is a standard test to measure pre-morbid IQ, was on average 119 (range 101 to 128) in 118 vegan men.

Vegans are a healthy lot.